Mark Zuckerberg is the founder of the site Facebook, you can have a look at each other’s

Mark Zuckerberg is the founder of the site Facebook, you can have a
look at each other’s pictures.
A. where
B. which
C. when
D. as

(答案→)A. whereB. whichC. whenD. as解析：这题考查定语从句的用法，where引导定语从句修饰Facebook，而且where在定语从句中做地点状语，句意是：Mark Zuckerberg 是Facebook的创始人，在facebook你可以看见彼此的照片。选A。

好好学习下