If headaches only occur at night, lack of fresh air and oxygen is often the cause.

如果头痛只发生在晚上，缺少新鲜空气和氧气常常是其原因。

《柯林斯英汉双解大词典》

Such a unique view can only occur during those few seconds where the existing moonlight balances with the almost unseen first rays of sunlight.

这种独特的景象只出现在那几秒之内，在那几秒内，原有的月光和几乎看不见的第一缕阳光相平衡。

youdao

For this reason, this phase should only occur after you have redesigned the process.

因此，此阶段仅应在您重新设计了流程之后进行。

youdao

The challenger contends that ballots marked for Mr.Karzai are arriving from districts where voting did not occur and turnout is being reported as high as 40 percent in areas where only 10 percent of voters cast ballots.

VOA: standard.2009.08.23

The only important thing to realize about that is that these differences start to occur very early in development.

唯一需要引起重视的是,这些差异发生在,发育阶段的早期

耶鲁公开课 - 生物医学工程探索课程节选

One of the big problems with studying human diseases is that you can study how they occur in people but there's only a limited amount that you can learn from people.

在人类疾病研究中的一个难题是,你有能力研究发病原因,但以人类为样本做研究却是备受限制

耶鲁公开课 - 生物医学工程探索课程节选

But this can only occur if the West can restore its belief in its future.

FORBES: The Poverty Of Ambition: Why The West Is Losing To China And India

You'll have the psychological dementia that only occur in co-op and really bring details out.

CNN: Horror journeys into the mind in 'Dead Space 3'

Change at the individual level can only occur when the culture and environment support it.

FORBES: Timing Is Everything