Without planning, some kinds of environment may not happen.

没有规划，某些环境可能不会发生。

youdao

If for any reason this does not happen, the ancestral feature may not disappear, leading to an atavism.

如果因为任何原因，这些事情没有发生，祖先的种种特性也许就不会消失，从而导致返祖现象。

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They may not happen as quickly as you'd like them to, and they may turn out to be completely different from the special things you imagined at the beginning, but they will happen.

它们可能也不会像你所希望的那样迅速发生，而且可能与你最初想象的特定事物完全不同，但它们终究会发生。

youdao

Still,many people argue that his talent should be recognized because ten national coaching victories do not happen by accident.

VOA: special.2009.07.10

So, electron promotion does not happen in terms of nitrogen, because it would not increased our number of unpaired electrons.

这里对于氮原子不会有电子激发，因为这不会增加,未配对电子的数目。

麻省理工公开课 - 化学原理课程节选

It might be true that those cases do happen, but I really think they are not the norm.

虽然有这种案例，但我并不认为这是一种普遍情况。

需要动物实验吗？ - SpeakingMax英语口语达人

Never events are defined by the CQC as serious, largely preventable incidents which should not happen.

BBC: Devon hospitals report serious surgical errors

Some fertility experts raised concerns that the expanded recommendations may not happen in reality.

BBC: IVF should be given sooner and to older women, says NICE

Her conclusion: the "year of the smart phone" might not happen until, say, 2011.

FORBES: In The Air