流产(abortion)
参考答案：
流产是指妊娠不足28周，胎儿体重不足1000g而终止者。
The students had to finish their homework on time, _______? [ ]
A. didn't they
B. must they
C. did they
D. hadn't they
单元测试中的对象为______。
A．功能模块
B．实现了具体功能的程序段
C．整个体系
D．概要设计中的单元
