--What about going to the South Lake for a picnic next weekend?--OK. But I’m not s

问题补充：

----- What about going to the South Lake for a picnic next weekend?

----- OK. But I’m not sure it will rain.

A. why

B. where

C. when

D. whether

答案：

A. why

B. where

C. when

(答案→)D. whether

解析：根据上下文可知，第二个人同意下周末去野餐，但又不能确定是否会下雨，故选D。