thickens
v.
（使）变厚（或粗、浓、密），使更厚（或更密、更浓、更粗）( thicken的第三人称单数 );
使（话等）不清晰，使模糊;
使（情节等）复杂;
变得不清晰，变得模糊;
例句:
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Cook the sauce over a low heat until it boils and thickens.
以小火加热酱汁至其沸腾变浓。
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Whisk together until the mixture thickens and forms an emulsion.
来自BBC
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"Find anything?" he asked. "Yeah. The plot thickens," I said.
“有什么发现没有？”他问。“嗯，情况越来越复杂了，”我说。
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Keep stirring until the sauce thickens.
不停地搅，一直搅到调味汁变稠。
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If the polenta thickens early, stir in some more water.
来自THETIMES
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Continue to whisk until the mixture thickens.
来自BBC