Most of students ........... how to use computer fluently up to now

1.Most of students ........... how to use computer fluently up to now.
A. have known B. knew C. has known D. know
2.They ........... the film before, so they stayed home.
A. were seeing B. saw C. were seen D. had seen
3.His light are out. Perhaps, he ........... to sleep.
A. is going B. has gone C. goes D. went
4.While ........... in the park, we found a purse full of money.
A. we are walking B. walk C. we walked D. we were
walking