Put the verb into the correct form, present simple or past

Put the verb into the correct form, present simple or past simple, active or passive.
1.It's a big factory. Five hundred people .................(employ) there.
2.Water.................(cover) most of the Earth's surface.
3.Most of the Earth's surface...............(cover) by water.
4.The park gates................(lock) at 6.30 p.m. every evening.
5.The latter.................(post) a week ago and it................(arrive) yesterday.
6.The boat................(sink) quickly but fortunately everybody.................(rescue).
7.Ron's parents..............(die) when he was very young. He and his sister................(bring) up by their grandparents.
8.I was born in London but I...............(grow) up in the north of England.
9.While I was on holiday, my camera................(steal) from my hotel room.
10.While I was on holiday, my camera...................(Disappear) from my hotel room.
11. Why................(Sue/resign) from her job? Didn't she enjoy it?
12.Why................(Bill/sank) from his job? What did he do wrong?
13.The company is not independent. It.................(own) by a mush larger company.
14.I saw an accident last night. Somebody..................(call) an ambulance but nobody..................(injure) so the ambulance..................(not/need).
15.Where..............(these photographs/take)? In London? .................(you/take) them?
И необходимо разъяснить, почему поставили в такой форме.
Пожалуйста!!!