We went to Mountain Tai last weekend, , not surprisingly, was crowded with visitors.
A. that
B. which
C. where
D. when
网友回答
A. that
(答案→)B. which
C. where
D. when
解析：这里从总的方面来看考查的非限制性定语从句，我们找到定语从句的先行词，根据空格后面的was crowded with visitors我们可以判断这个定语从句的先行词应该是在山上人有很多而不是指时间，所以不能用when。