react          
verb [ I ] uk/riˈækt/ us/riˈækt/
B2 反应;作出回应
to act in a particular way as a direct result of something else
  She slapped him and called him names, but he didn't react. 她打他并辱骂他,但他不予回应。 
 The judge reacted angrily to the suggestion that it hadn't been a fair trial. 有人说审判不公正,法官对此很愤怒。 
 Many people react (badly) to (= are made ill by) penicillin. 很多人对青霉素(严重)过敏。 
  chemistry 产生(化学)反应
to change in a physical or chemical way when put with another substance
  Potassium reacts with water. 钾和水会发生化学反应。 
 - More examples
 - It's difficult to gauge how they'll react.
 - She slapped him and called him names, but he didn't react.
 - The prime minister reacted angrily to claims that he had lied to the House of Commons.
 - She reacted surprisingly calmly to the news of his death.
 - The government was very slow to react to the problem.
 
Phrasal verb   
react against somethingC2 抗拒;反抗;反对
to intentionally do the opposite of what someone wants you to do because you do not like their rules or ideas
  He reacted against everything he had been taught. 教他什么他都会唱对台戏。