15.
1 is reading
2 is working
3 is not delivering
4 is writing
5 am preparing
6 are working
7 is sitting
8 is not going
9 is standing
10 What are you doing?
16.
1 My sister isn't playing the piano now.
Is my sister playing the piano now?
2 The teacher isn't explaining the rule.
Is the teacher explaining the rule?
3 We are not learning the new words.
Are we learning new words?
4 Ann is not standing at the window.
Is Ann standing at the window?