It was _____ back home after the experiments.[ ]

A. not until midnight did he go

B. until midnight that he didn't go

C. not until midnight that he went

D. until midnight when he went

自然选择学说指出：在自然界，各种生物普遍具有很强的______能力，能能够产生大量后代，而生物赖以生存的______和空间都是非常有限的．任何生物要生存下去，就得为此进行______斗争．在这个过程中，只有那些具有______变异的个体才容易生存下来，并将这些变异传给下一代，而具有______变异的个体则容易被淘汰．