突然下起大雨的时候，你在做什么？

What were you doing when the heavy rain suddenly came?

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比赛才刚刚开始，就突然下起倾盆大雨，于是比赛暂停。

The match had just begun when the heavens opened and play was suspended.

《柯林斯英汉双解大词典》

果然，到了中午，下起了倾盆大雨。

Sure enough, by noon the rain was pouring down.

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And in the meantime the rain had become a voluptuous shower.

这时外面下起了大雨。

耶鲁公开课 - 1945年后的美国小说课程节选