The answer is :
1) The girls aren't riding their bikes.
2) He isn't taking out a book.
3) I am not washing my hair.
4) The baby isn't crying.
5) You aren't listening to music.
6) The dog isn't running after the cat.
7) She isn't sitting on the chair.
8) My mum isn't preparing lunch now.
9) We aren't carrying buckets.
10) The teacher isn't opening the window.