2.

a. we can not .... because the water...

b. the company ... because it is ....

c. since we want ... we have

d. as the area..., no one ....

e. it started ... as we could not ...

f. mr minh... as he dedicated...

=>

a. Because the water is highly polluted, we cannot swim in this part of the river.

b. The company does not produce recycled paper since it is more expensive to produce it than regular paper.

c. As we want people to be aware of the problem of pollution, we have "a green week" three times a year.

d. Because the area around the beach is full of trash, no one wants to go swimming or sunbathing there.

e. Because it started to rain, we could not keep on cleaning the beach.

f. Mr. Minh is admired because he dedicates all his life to protecting the environment.