重点讲解：
1. a series of
一连串；一系列；连续；接连；
eg. A series of mischance happened.
一连串不幸的事发生了。
eg. The student always asks his teacher a series of questions.
这个学生总是问他老师一连串的问题。
2. serve to do
用作；充作；
eg. Their brief visit has served to underline the deep differences between the two countries.
他们短暂的访问恰恰凸显了两国间分歧的严重程度。
eg. A single example will serve to illustrate the point.
只举一个例子就可以把问题说清楚了。
3. range between
（在一定幅度内）变化，变动；
eg. Prices range between 7 and 10.
售价在7英镑和10英镑之间。
eg. The temperature ranges between 30 and 40 degrees centigrade.
温度在摄氏三十度与四十度之间。