we are young we can still do something to help protect the environment.A. IfB. SinceC. B

问题补充：

we are young, we can still do something to help protect the environment.

A. If

B. Since

C. Because

D. Though

答案：

A. If

B. Since

C. Because

(答案→)D. Though

解析：本题的含义是我们虽然小，但我们依旧可以做一些事保护环境，从句表示是让步，选项中though是尽管的意思，表示让步，故选D。