Which of the following can be the best title of the passage?

Which of the following can be the best title of the passage?

A.But that is exactly what we do.

B.This can provide ready access to clean water.

C.There is no longer any good reason to waste any type of water.

D.A “constructed wetland environment” is already in practice on a small scale .

E.This would reduce the need for fresh water for irrigation and energy for pumping.

F.If collected and treated properly, it could provide new water, fertilizer, and energy.

G.Although waste-water systems in large cities are effective ,the whole procedure usually costs much.

正确答案是AFGDE