1 This echo-location in bats is often compared with radar, the principle of WHICH is similar.

后半段有些让人迷惑，是不是先单独看WHICH，然后把“the principle of WHICH”看作一个单位，主语，但是PRINCIPLE又是单数。或者另一种解释：“WHICH is similar. ”是一个整体。

2 Parents have to do much less for their children today than they used to do, and home has become much less OF A WORKSHOP.

是不是“ OF A WORKSHOP ”在这里作形容词了？

3 In textile areas it has long been customary for mothers to go out to work, but this practice has become so widespread that the working mother is now A NOT unusual factor in a child's home life, the number of married women in employment having more than doubled in the last twenty-five years.

这个地方“A NOT”真是很奇怪。

1. 逗号以后是非限制性定语从句，which代表radar
2. of与become有关，整个儿不是形容词；仍是prep+n
3. 说怪不怪。a 与factor有关，not 修饰unusual。按双重否定理解