1.Rita is writing a story.

Question

2.I was buying vegetables.
3.seema was eating apples.
4. The family was watching a cricket match.

Answer 1

All four are in active voice. That is, the subject is doing the action.
http://www.chompchomp.com/terms/actionverb.htm

Now you need to turn each sentence around and convert the verb to passive voice. ~~> The subject will NOT be doing the action of the verb.
http://www.englishclub.com/grammar/verbs-voice-passive.htm

I'll do the first one; then you do the rest, and I'll check your work.

Rita is writing a story.
A story is being written by Rita.

Answer 2

Vna
Vhuii