Make the sentences negative I have been to Moscow. He saw them last year

1. I have been to Moscow.
   I have not been to Moscow.
   Сокращённо: I haven’t been to Moscow.

2. He saw them last year.
   He did not see them last year.
   Сокращённо: He didn’t see them last year.

Во втором предложении используется did not, потому что это Past Simple. После did not основной глагол ставится в начальную форму: saw → see.