each of which 用法

each of which 在以下為 同位語，非關代。

1. An urn contains two balls, each of which is known to be either white or black.

2. Q. Many companies set a number of objectives, ________ is an indicator of how well the company is performing.

(A) each (B) which (C) each of which (D) it

each of which 用法

原文：http://www.cnblogs.com/bittorrent/p/4035264.html