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caffeine + be found in + [food/drink]
用于说明咖啡因的来源，常用于科普或日常说明。
Caffeine is found in coffee and tea.
咖啡因存在于咖啡和茶中。
咖啡因；咖啡碱
先理解核心含义，再看它在真实句子里的用法。
咖啡因；咖啡碱
a bitter alkaloid found in coffee and tea that is responsible for their stimulating effects
Caffeine is found in coffee and tea.
咖啡因存在于咖啡和茶中。
一种生物碱,C8H10N4O2,天然存在于茶树和咖啡树中,对中枢神经系统有轻度刺激作用。
An alkaloid, C8H10N4O2, found naturally in tea and coffee plants, which acts as a mild stimulant on the central nervous system.
Drinking coffee late at night keeps me awake because of the caffeine.
深夜喝咖啡让我睡不着，因为里面有咖啡因。
If you are sensitive to caffeine, try switching to decaffeinated tea.
如果你对咖啡因敏感，试试改喝无咖啡因的茶。
The label says this energy drink contains about eighty milligrams of caffeine per can.
标签上说这种能量饮料每罐含约八十毫克咖啡因。
用于说明咖啡因的来源，常用于科普或日常说明。
Caffeine is found in coffee and tea.
咖啡因存在于咖啡和茶中。
用于解释因果关系，句型较正式。
Caffeine is responsible for the stimulating effects of these drinks.
咖啡因是这些饮品产生提神作用的原因。
Not this
I need a caffeine to stay awake.
Use this
I need caffeine to stay awake.
caffeine 是不可数名词，不能直接与不定冠词 a 连用；要表示“一杯含咖啡因的饮品”可说 a caffeinated drink 或 a cup of coffee.
Not this
I only drink caffeine coffee in the morning.
Use this
I only drink caffeinated coffee in the morning.
修饰饮品表示“含咖啡因的”要用形容词 caffeinated，caffeine 是名词，不能直接作定语修饰 coffee；也可说 coffee with caffeine，但最小改动是用 caffeinated.
Not this
The caffeine of green tea makes me alert.
Use this
The caffeine in green tea makes me alert.
表示“某物中的咖啡因”应用介词 in 表包含关系，of 表示所属关系在此不自然；这是中文“的”字结构的直译导致的问题.
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
咖啡因含量
The label lists the caffeine content of the drink.
标签上列出了这种饮料的咖啡因含量。
咖啡因摄入量
Doctors recommend limiting your caffeine intake in the afternoon.
医生建议你在下午限制咖啡因的摄入。
咖啡因戒断
Her headache was caused by caffeine withdrawal after she quit coffee.
她戒掉咖啡后，头痛是由咖啡因戒断引起的。
咖啡因敏感性
His caffeine sensitivity means he cannot drink soda after dinner.
他对咖啡因敏感，所以晚饭后不能喝汽水。
咖啡因带来的兴奋感
I need a caffeine buzz to wake up in the morning.
我早上需要咖啡因带来的兴奋感来提神。
咖啡因成瘾
Caffeine addiction is difficult to break.
咖啡因成瘾很难戒除。
咖啡因提神（指满足对咖啡因渴求的一杯咖啡等）
I need my morning caffeine fix before I can function.
我需要早上喝杯咖啡因提神才能正常工作。
咖啡因带来的兴奋感
She was so energetic after that caffeine buzz.
喝了咖啡因后她兴奋得不得了。
咖啡因失效后的疲惫感
He hit a caffeine crash in the afternoon and couldn't stay awake.
他下午咖啡因劲头过了，困得睁不开眼。
Use caffeine naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
读音近似“咖啡因”，咖啡中让人提神的成分就是 caffeine——记住“咖啡因”三个字即可。
语域：neutral 常见场景：everyday conversation、scientific writing、food and drink labels 该词通常为中性用法，日常对话、科普文章和产品说明中都比较常见，无明显的正式或非正式倾向。
通常作不可数名词；表示不同种类时可用复数形式 caffeines。
Dictionary facts from ECDICT, WIKTIONARY.