Correct Answer: B. I haven't seen her for a week.

• Explanation: This sentence correctly uses the present perfect tense to indicate that you have not seen her for the duration of one week.

Why not the others?

• A: Incorrect because "have seen" with a specific time ("a week ago") is grammatically incorrect.
• C: Incorrect because "since a week" is not proper English; it should be "since last week."
• D: Incorrect because "didn't see her for a week" implies the action happened in the past and is now over, which doesn't match the context.

Correct Answer: A. He spent three hours finishing his homework yesterday.

• Explanation: "Spent" is the correct verb to express the duration of an activity, and "finishing" is the correct form following "spent."

Why not the others?

• B: Repeats the original sentence instead of rephrasing.
• C: Incorrect because "spent" should be followed by the -ing form ("finishing"), not "to finish."
• D: Incorrect because "spent three hours finish" is grammatically incorrect; it should be "finishing."