It's eight now. It's time _______.
A:go to school
B:go to the bed
C:to go to school
D:go home
假定基因A是视网膜正常所必需的,基因B是视神经正常所必需的。现有基因型为AaBb的双亲,从理论上分析,他们所生的后代视觉正常的可能性是( )
下图是《说文解字》列出的“历”“史”二字的篆书。许慎解释道,“历”者,过也,传也。“史”者,记事者也,从又持中;中,正也。据此可知,“历史”的原意是指( )