動詞 react:

1. show a response or a reaction to something
   同義詞：respond
2. undergo a chemical reaction; react with another substance under certain conditions
3. act against or in opposition to
   同義詞：oppose

1. Iron reacts with water and air to produce rust.
   鐵與水和空氣起化學反應而生銹。
2. She reacted to the insult by turning her back on him.
   她受辱之后就不再理睬他了。
3. How did they react to your suggestion?
   他們對你的建議有什么反應？
4. An acid can react with a base to form a salt.
   酸可以和堿起反應而生成鹽。

re.act

v.intr.（不及物動詞）
re.act.ed,re.act.ing,re.acts
To act in response to or under the influence of a stimulus or prompting:
反應，作出反應：在某種刺激或提示的影響下或針對這種影響而采取的行動：
例句：
reacted strongly to the sarcastic tone of the memorandum.
對于備忘錄所使用的諷刺性口吻而作出強烈反應

To act in opposition to a former condition or act:
背離，反其道而行：以與以前條件或行為相反的方式行動：
例句：
composers who reacted against romanticism.
背離浪漫主義的作風家

To act reciprocally or in return.
反作用：相對地或還原性作用
Chemistry To undergo a reaction:
【化學】 起化學作用：產(chǎn)生化學反應：
例句：
Methane reacts with hydroxyl to produce formaldehyde.
甲烷與羥基反應生成甲醛