They last saw each other six months ago.
Correct answer: A
Knowledge: Present perfect tense
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