Question

_____(protect)the environment,they will plant more trees along the lake

Answer 1

__To_ protect__(protect)the environment,they will plant more trees along the lake
不定式作目的状语

为了保护环境，他们将沿着湖种许多树。

祝你学习进步~！

Answer 2

To protect
解释：动词不定式作目的状语。

祝你学习进步，更上一层楼！请记得采纳，谢谢！(*^__^*)