重点讲解：
1. be composed of 组成；构成；
All animals and plants are composed of cells.
一切动植物均由细胞组成(pO1GRMzDwXsItjP。
2. concentrate on 全神贯注;集中（心思）；
I am leaving to concentrate on writing fiction.
我辞职是为了专心写小说a+&3Ruh3isk。
3. hail from （人或物）来自；
They hail from all parts of the country.
他们来自全国各地=tAHJnfn1.wem#];,~7。
4. be dependent on 取决（于…）的；有赖（于…）的；
Up to two million people there are dependent on food aid.
那里有多达200万人口依靠食品援助EN%#!oolV5Us。