MLS-C01 Exploratory Data Analysis Practice Question
This MLS-C01 practice question tests your understanding of exploratory data analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Network Topology
A data scientist is exploring a dataset stored as a single 2 GB object in S3. The scientist wants to read only a subset of the file (e.g., the first 1000 lines) to perform initial data inspection. Which approach should the scientist take to minimize data transfer and cost?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Network Topology
A
Use the AWS CLI to download the entire file and then use head to get the first lines.
Why wrong: Downloading the entire 2 GB file is costly and slow.
B
Use S3 Select with a SQL query to retrieve the first 1000 rows.
S3 Select efficiently retrieves only the required subset.
C
Use the S3 Range header to read the first 1 MB of the file and parse lines.
Why wrong: Range read may not align with line boundaries and still transfers data.
D
Use Amazon Athena to query the file with LIMIT 1000.
Why wrong: Athena scans the entire file, incurring full cost.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use S3 Select with a SQL query to retrieve the first 1000 rows.
Option B is correct because S3 Select enables retrieving a subset of data using SQL queries, such as SELECT * FROM s3object LIMIT 1000, minimizing data transfer and cost. Option A is inefficient as it downloads the entire 2 GB file. Option C retrieves bytes, not lines, and may still transfer excessive data or require multiple requests to locate line boundaries. Option D scans the entire file with Athena, incurring cost and latency for a full table scan even with LIMIT 1000.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use the AWS CLI to download the entire file and then use head to get the first lines.
Why it's wrong here
Downloading the entire 2 GB file is costly and slow.
✓
Use S3 Select with a SQL query to retrieve the first 1000 rows.
Why this is correct
S3 Select efficiently retrieves only the required subset.
Clue confirmation
The clue words "first", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use the S3 Range header to read the first 1 MB of the file and parse lines.
Why it's wrong here
Range read may not align with line boundaries and still transfers data.
✗
Use Amazon Athena to query the file with LIMIT 1000.
Why it's wrong here
Athena scans the entire file, incurring full cost.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
Quick reference
AWS S3 Storage Class Comparison
Storage Class
Min Duration
Retrieval
Use Case
S3 Standard
None
Immediate
Frequently accessed data
S3 Standard-IA
30 days
Immediate
Infrequent access, rapid retrieval
S3 One Zone-IA
30 days
Immediate
Non-critical infrequent data
S3 Intelligent-Tiering
None
Immediate–hours
Unknown or changing access patterns
S3 Glacier Instant
90 days
Milliseconds
Archive with instant retrieval
S3 Glacier Flexible
90 days
Minutes–hours
Archive, flexible retrieval
S3 Glacier Deep Archive
180 days
Hours
Long-term compliance archive
What to study next
Got this wrong? Here's your next step.
Identify which MLS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Exploratory Data Analysis — This question tests Exploratory Data Analysis — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use S3 Select with a SQL query to retrieve the first 1000 rows. — Option B is correct because S3 Select enables retrieving a subset of data using SQL queries, such as SELECT * FROM s3object LIMIT 1000, minimizing data transfer and cost. Option A is inefficient as it downloads the entire 2 GB file. Option C retrieves bytes, not lines, and may still transfer excessive data or require multiple requests to locate line boundaries. Option D scans the entire file with Athena, incurring cost and latency for a full table scan even with LIMIT 1000.
What should I do if I get this MLS-C01 question wrong?
Identify which MLS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "first", "minimum / minimize". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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