Default DROP blocks all; allow only HTTP/HTTPS.
Why this answer
Option C is correct because it sets the default policy for the INPUT chain to DROP, which blocks all incoming traffic by default, and then explicitly adds rules to ACCEPT TCP traffic on ports 80 (HTTP) and 443 (HTTPS). This implements a whitelist approach: only the specified services are allowed, and all other incoming packets are dropped by the default policy. The order is critical — the ACCEPT rules must be evaluated before the default DROP policy takes effect for unmatched traffic.
Exam trap
The trap here is that candidates often confuse the default policy with explicit rules, thinking that setting a default ACCEPT and then adding a DROP rule at the end will block all other traffic, but the default policy is evaluated only after all rules are checked, so a default ACCEPT will allow unmatched traffic regardless of a final DROP rule.
How to eliminate wrong answers
Option A is wrong because it sets the default policy to DROP but then adds a rule that accepts all TCP traffic regardless of destination port, which would allow all TCP-based traffic (including SSH, SMTP, etc.), not just HTTP and HTTPS. Option B is wrong because it sets the default policy to ACCEPT, which allows all incoming traffic by default, and then adds ACCEPT rules for ports 80 and 443 (which are redundant since the default already accepts everything), and finally adds a DROP rule that would only affect packets not matched by the earlier ACCEPT rules — but because the default policy is ACCEPT, the final DROP rule is effectively useless for traffic that doesn't match the earlier rules (since the default already accepts it). Option D is wrong because it sets the default policy to ACCEPT, which permits all incoming traffic, and then adds ACCEPT rules for ports 80 and 443 (which are unnecessary), but does not include any rule to block other traffic, so all incoming traffic is allowed.