(a) negative
I have not finished the work.
He has not written a letter.
The cat has not drunk its milk.
They have not understood the lesson.
Richard has not gone to the Zoo.
I did not finish the work yesterday.
He did not write a letter last week.
Richard did not go to the Zoo last week.
(b) interrogative
Have I finished the work?
Has he written a letter?
Has the cat drunk its milk?
Have they understood the lesson?
Has Richard gone to the Zoo?
Did I finish the work yesterday?
Did he write a letter last week?
Did Richard go to the Zoo last week?