Ecologists are trying to preserve our environment for future generations by protecting the ozone layer, purifying the air, and have planted the trees that have been cut down.

24/30

Ecologists are tryingto preserve our environmentfor future generations by protecting the ozone layer, purifying the air, and have planted the trees that have been cut down.

(A) To preserve

(B) For

(D) Have planted

Giải thích

Chọn đáp án D ⇒ planting

Giải thích: các động từ theo sau “by” được nối với nhau bởi “and” nên được chia Ving giống nhau (protecting, purifying)