1 [C, U] ~ (to sb/sth) response to a situation, an act, an influence, etc （对情况、行动、影响等做出的）反应, 回应
*What was his reaction to the news? 他对这消息的反应如何?
* Her arrest produced an immediate/a sudden reaction from the press. 她被捕的事立刻[突然]在新闻界引起反响.
* the shocked reaction of schools to education cuts 学校对削减教育经费的激烈反应
* Reaction to his taunts will only encourage him. 别理会他恶言寻衅, 一理他更来劲儿.
2 [sing] physical response, usu a bad one, to a drug, chemical substance, etc （由药物、化学物质等引起的）生理上的反应（通常指不良反应）
*an allergic reaction to animals, birds, etc 对兽类、鸟类等的变态反应
* I had a bad reaction after my typhoid injection. 我注射伤寒针剂後产生了不良反应.
3 [sing, U] return to a previous state after a period of the opposite condition 回复到原来的状态; 复旧
*After all the excitement there was (an inevitable) reaction, eg a time when life seemed dull again. 热闹一番过後, （不可避免地）又恢复了旧观（生活沉闷如故）.
4 [U] opposition to (esp political) progress or reform 反对（尤指政治的）进步或改革; 反动
*The forces of reaction made reform difficult. 反动势力给改革造成了困难.
5 [C, U] chemical change producedby two or more substances acting upon each other 化学反应
*nuclear reaction, ie change within the nucleus of an atom 核反应.
1【to a situation/event】2【moving quickly】3【to food/drugs】4【science】5【change】6【against change】
【TO A SITUATION/EVENT】 [U and C]
something that you feel or do because of something that has happened or been said
→response What was Jeff's reaction when you told him about the job?reaction to the government's reaction to the fuel crisisbring/provoke/produce a reaction The news brought an angry reaction from unions.sb's first/immediate reaction His first reaction was to deny everything.instinctive/gut reaction
(=what you immediately feel before you have time to think) My gut reaction was not to trust him. There were mixed reactions (=different people reacting in different ways) to the strike.in reaction to sth An emergency fund was set up in reaction to the famine.【MOVING QUICKLY】reactions [plural]
your ability to move quickly when something dangerous happens suddenly a skilled driver with very quick reactions【TO FOOD/DRUGS】[C]
if you have a reaction to a drug or to something you have eaten, it makes you illreaction to a reaction to the immunizationhave/suffer a reaction She had a severe allergic reaction to the drug.cause/bring on/trigger a reaction Certain foods are more likely than others to cause allergic reactions .【SCIENCE】 [U and C]a)
a chemical change that happens when two or more substances are mixed together a chemical reaction in the soilb)
a physical force that is the result of an equally strong physical force in the opposite direction【CHANGE】 [singular]
a change in people's attitudes, behaviour, fashions etc that happens because they disapprove of the way in which things were done in the pastreaction against a reaction against the traditional values of the nineteenth century【AGAINST CHANGE】[U]formal
strong and unreasonable opposition to all social and political changes The revolutionary movement was crushed by the forces of reaction .
1. What was his reaction to the news? 他对这消息的反应如何?
2. The poor record of survival, plus public reaction against the media´s use of heart transplants for publicity (and perhaps also entertainment), gave rise to a wave of anti-transplant feelings both in and outside the medical profession. 由于手术后病人存活时间短，加之公共舆论反对新闻界利用心脏移植来进行宣传（甚至娱乐），所以，医学界内外掀起了一股反对心脏移植的浪潮。
3. This boost in reaction time after exercise training may occur because declines associated with getting old could actually stem from declines in physical condition. 接受运动训练之后，人的反应速度会加快，这可能是因为与衰老有关的机能衰退实际上根源于体质下降。
4. That's an understandable reaction. 这种反应是可以理解的。
5. There was a sudden drop in activity in the left side of the brain — the side most involved in language — and an exaggerated reaction on the right, the side strongest at thinking about the location of objects. 他们的左半脑 -- 与语言能力相关的那一半 -- 的活动急剧下降，而右半脑，擅长思考物体方位的那一半，却做出强烈的反应。
6. Notice a person's reaction to stress in these situations and to aggressive behavior in others. 请注意一个人在这类情况下遇到压力时的反应，以及他/她在其他情况下遇到挑衅性行为时的反应。
7. His initial reaction was one of shock. 他最初的反应是震惊。
8. If parents were prepared for this adolescent reaction, and realized that it was a sign that the child was growing up and developing valuable powers of observation and independent judgment, 如果家长对青少年的这种反应有思想准备，并且意识到这象征着孩子们正在成熟和正在发展宝贵的观察力、独立判断力，
9. Frequently the reaction it causes is only a skin rash or a light fever. 通常只是皮疹、低烧。