The illness is triggered by a chemical imbalance in the brain.

该病是由大脑里一种化学失衡引发的。

《柯林斯英汉双解大词典》

Experiments have also cast serious doubt on the belief that yawning is triggered by a drop in blood oxygen or a rise in blood carbon dioxide.

对于打哈欠是由血液中的氧气减少或血液中的二氧化碳增加引起的这种观点，一些实验也同样提出了严重的质疑。

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Acne is triggered by puberty hormones.

青春痘是由青春期激素引发的。

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One set of subsidies is triggered by prices that Congress sets in farm bills.

NPR: Groups Push for End to Crop Subsidies

Folklore is correct that yawning is triggered by boredom, drowsiness, stretching or other people yawning.

WSJ: Matt Ridley on Why You Just Yawned | Mind & Matter

Bleaching is triggered by high temperatures and its frequency has increased, probably in response to global warming.

ECONOMIST: The Great Barrier Reef: Dr De��ath v the killer starfish | The