重点讲解：
1. perch on 栖息；在较高或较险的位置
例句：Tall buildings perch on the top of rocky cliffs.
高耸的建筑屹立在嶙峋的悬崖顶上。

2.rain down 如雨般落下
例句：If one Ford works as planned, a series of benefits will rain down on the company and its suppliers.
如果Ford一体化如计划般展开，一系列的盈利就会降临到公司和供应商头上。

3.form into 组成；编成
例句：The single piece of DNA molecule winds itself around special proteins to form into very tight coils like a string (shown in yellow).
这个一段DNA分子把自己弯曲在特殊的蛋白质周围而形成非常紧的卷如一段弦一样（如黄色部分所示）。

4.pull apart 扯断(索子等)；劝开
例句：These pieces of ice don't pull apart easily.
这些冰块不易分开。