He doesn’t know they will plant trees on Saturday or not.A. weatherB. whether C. ifD. tha

问题补充：

He doesn’t know they will plant trees on Saturday or not.

A. weather

B. whether

C. if

D. that

答案：

A. weather

(答案→)B. whether

C. if

D. that

解析：考查固定搭配。Whether...or not“是否......”，句意“他不知道周六他们是否去种树。”故选B。