They last saw each other six months ago.

Knowledge: Present perfect tense

Explain:

The present perfect is used to describe an action that happened in the past but the result still affects the present.

Formula: S + have/has Ved/V3 + for + time period/since + timeline

How to rewrite sentences with present perfect tense:

S + last + Ved + time ago. = S + haven’t/ hasn’t Ved/V3 + for time period.

They last met 6 months ago.

= A. They haven’t seen each other in six months.

B. is wrong in “since six months” (6 months is the period, must use “for”)

C. They met for six months. => wrong in meaning

D. They hadn’t seen each other six months ago. => wrong in meaning

Choose A