vera911213
举例说明：
The factory was built in a secret place, around ____ high mountains.
A.which was B.it was C. which were D. them were
有很多同学会误选“A或者B”，原因在于他们知道题干中后半句缺少的是主语，因此只要填补主语就可以使句子变完整（这一步判定是正确的），但是为什么不能选择上面两项呢？
A的错误在于没有分清名词的单复数，既然后面有high mountains，结尾是“s”,那么谓语动词也应该用复数，A选项was显然不对，因此排除A；
B选项在于没有弄清楚题干的句型种类，本句实际上考察的是非限制性定语从句，因此连词应当选择which，排除B和D，这样我们就可以得出答案是C。
around which were high mountains是一个由“介词+which”引出的非限制性定语从句，而在本句中，主语是high mountains， around which 是表语，所以句子谓语应该用复数were，
