要防止铸坯产生裂纹必须将钢中磷、硫之和控制在（）以下。
A、0.050%
B、0.50%
C、0.0050%
D、0.10%
参考答案：A
The school was moved out of downtown as the number of students had grown too _____. [ ]
A. small
B. few
C. large
D. many
下列组成中不属于交流发电机的是（）。
A.定子
B.转子
C.整流器
D.换向器
