Which of the following is NOT the cause of childless couples？
A. They are too busy with their work.
B. They may not be good parents.
C. They want to be free from the family responsibilities.
D. They are physically unable to have children.
Which statement is NOT TRUE？
A. The earliest men differed from men today.
B. Modern man has developed from a simpler animal of its kind.
C. The earliest men had much smaller brains than men today.
D. A large number of the earliest men have also survived though they were weaker.
15，35，63，()
A. 78
B. 99
C. 81
D. 100
某车工计划15天里加工420个零件，最初3天中每天加工24个，以后每天至少要加工多少个才能在规定的时间内本额本完成任务？()
A. 31
B. 29
C. 30
D. 28
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