The answer is that the query is trying to read data from the 'sensitive/' prefix. This is the most likely reason because the IAM policy includes a Deny on s3:GetObject for that specific prefix, and Athena requires s3:GetObject permissions to read the underlying data files in S3 when executing a query. Even though the policy allows s3:ListBucket, the explicit Deny on GetObject for objects under 'sensitive/' overrides any Allow, causing the access denied error when Athena attempts to retrieve data from that location. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of how IAM policy evaluation logic works with Athena’s S3 access patterns—a common trap is assuming that listing permissions are sufficient for query execution. Remember, Athena needs both ListBucket and GetObject; a Deny on GetObject for a specific prefix will block any query that touches that data. Memory tip: “Deny always wins—if Athena can’t GetObject, your query is dead on arrival.”
MLS-C01 Exploratory Data Analysis Practice Question
This MLS-C01 practice question tests your understanding of exploratory data analysis. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An IAM policy is attached to a data scientist's role. The scientist is trying to list objects in the 'data-bucket' using Amazon Athena. The query fails with an access denied error. What is the MOST likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The query is trying to read data from the 'sensitive/' prefix.
Option B is correct because Athena needs s3:GetObject on the bucket to read data, but the Deny statement prevents access to objects under 'sensitive/' prefix. However, the query may be trying to read from that prefix. Option A is wrong because ListBucket is allowed. Option C is wrong because Deny blocks GetObject. Option D is wrong because the policy is valid.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The policy does not allow s3:ListBucket on the bucket.
Why it's wrong here
ListBucket is allowed.
✗
The policy has a syntax error.
Why it's wrong here
Policy is valid.
✓
The query is trying to read data from the 'sensitive/' prefix.
Why this is correct
Deny overrides Allow for that prefix.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The s3:GetObject action is explicitly denied for all objects.
Why it's wrong here
Only denied for 'sensitive/' prefix.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related MLS-C01 ACL questions on filtering logic and placement.
Exploratory Data Analysis — This question tests Exploratory Data Analysis — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The query is trying to read data from the 'sensitive/' prefix. — Option B is correct because Athena needs s3:GetObject on the bucket to read data, but the Deny statement prevents access to objects under 'sensitive/' prefix. However, the query may be trying to read from that prefix. Option A is wrong because ListBucket is allowed. Option C is wrong because Deny blocks GetObject. Option D is wrong because the policy is valid.
What should I do if I get this MLS-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related MLS-C01 ACL questions on filtering logic and placement.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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