单位骤冷因数
参考答案：
单位骤冷因数就是水骤冷因数＝水骤冷时间（min）/焦炭产量（t）。
There are fifty students in our class, ______ of them are girls.[ ]
A. two third
B. second three
C. two thirds
填空
1. His family _____ （be）very big. There are six people.
2. My family _____ (be) very well.
