问题
选择题
The buses, _____ were already full, were surrounded by anxious people.
A．all of them
B．all of which
C．they all
D．all which
答案
答案：B
题目分析：句意：公共汽车，已经都满了，被焦急的人群包围。这里含有一个定语从句，分析句子结构可知，该空所填词用来引导定语从句，选B。
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分别表示三种元素的原子，那么有下面四幅图表示构成物质的粒子