of which 用法

题目

of which 用法
There are over 58,000 rockey objects in space,about___ could fall down onto the earth.
A.900 of which
B.of which 900
我好想记得我们老师说过of which about
为什么

答案

A
of　表示整体当中的一部分.about 900 of which在这里可以换成of which about 900.因为介词+关系代词可以引导定语从句.
如果表示的是所属关系,则有四种说法.如：
The house whose window faces south is beautiful. 窗户朝南的这栋房子很漂亮.
＝The house the window of which faces south is beautiful.
= The house of which the window faces south is beautiful.
=The house which the window of faces south is beautiful.