题目内容

Throughout most of their lives, human beings perpetually learn and increase their mental capacities().

A. actually
B. readily
C. finally
D. constantly

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There()no further business to discuss, we all went home.

A. is
B. was
C. being
D. would be

We have to ask them to quit talking in order that all people present could hear us clearly().

A. decrease
B. cease
C. continue
D. keep

具有一对杂合基因的个体连续自交______代，才能使约97%的个体纯合。

A. 3
B. 5
C. 6
D. 7

玉米n+1的花粉不育，n+1的胚囊可育，已知R产生红色，r无色。在杂交RRr♀×rr♂中子代的表现型比例是______。

A. 1红:1无
B. 3红:1无
C. 5红:1无
D. 6红:1无