Ответ:

1. I have been waiting here for 2 hours (positive)

I haven't been waiting here for 2 hours (negative)

Have I been waiting here for 2 hours? (question)

2. Mary has been cooking tasty dishes for 2 hours (positive)

Mary has not been cooking tasty dishes for 2 hours (negative)

Has Mary been cooking tasty dishes for 2 hours? (question)

3. Has Sam been shopping for 3 hours? (question)

Sam has been shopping for 3 hours (positive)

Sam has not been shopping for 3 hours (negative)