Complet each blank with one given word. There are more words than needed

Part 1:Complet  each blank with one given word.There are more words than needed.

of  which  where  have  because  on  though  pollution

1.Viet Nam,..................... os in south-east Asia,exports a lot of rice

2,I don't believe UFOs exist ....................articles and reports in newspapers talk lots about UFO appearance.

3.Do whatever you can to conserve oil ............................. oil is a valuable resource

4.You shouldn't leave lights,air-conditioners and televisions ................... when no one is in the room

5.It's very kind .................you to help me