1,Nick sneezed so much because of the dirty air.
The dirty air made...........................................
2,There are a lot of trees .The air clean. 
If........................................................................
3,Volunteers have given out food and blankets to homeless people.
Food and blankets............................................ 
4,Most people left before the volcano erupted.
After................................................................. 
5,There is so much light in the city at night, so we can't see the stars clearly.
If....................................................................
6,Because the water is polluted, the fish are dead.(viết lại câu dùng due to)
.........................................................................
7, Everyone litters, so the environment is polluted (nối dùng because) 
......................................................................
8,What had you done before going to bed last night.(trả lời câu hỏi) 
.....................................................................