1Respond or behave in a particular way in response to something.

市场的反应是又下跌了3.1%。

1. 1.1react against Respond with hostility, opposition, or a contrary course of action to.
   敌视；反对；与…反其道而行之
   they reacted against the elite art music of their time

   他们摒弃当时的高雅艺术音乐，另搞一套。

   Example sentencesExamples

   • I cannot help reacting against all the negative criticism of the regime that one hears in England.
   • ‘We've reacted against what's happened in those big studios,’ says Shaw.
   • Third, many people in the younger generation, under age 30 or so, are reacting against the culture of divorce.
   • How do we react against such violence and war in our time?
   • We were reacting against bands we considered to be turgid and boring.
   • He is a player who gets a lot of challenges against him and he has to resist reacting against them and keep playing the game.
   • And, once again, traditionalists are reacting against globalization just as vehemently, if not more so, as they did against modernity.
   • So post-punk is music which is reacting against punk, consciously trying to move beyond it.
   • In part, that is what Muslim fundamentalists are reacting against.
   • Whether you are repeating them or reacting against them could be explored further.
   • The French have reacted against a document they think is an Anglo-Saxon plot to move away from a ‘social’ Europe.
   • Workers reacted against the outrageous contract demands of the company, voting by an overwhelming 48 to 3 for strike action.
   • Plus, people who fervently believe in stupid ideas have a quite consistent track record into reacting against dissent with violence.
   • But at least it tried to offer what it thought was a coherent alternative to the society it was reacting against.
   • Superficially he reacted against this background.
   • There appears to be a growing disquiet about the recent actions and opinions of America that many people are reacting against.
   • It seems to be reacting against the conventional attitudes of intellectuals at least those raised in the Western tradition.
   • A lot of the Victoria bands that started around 2000 were reacting against the insular hardcore scene out there.
   • The positive side being, they could not be stopped from reacting against portions they disliked.
   • The second neat thing we learn is that the rioters aren't reacting against capitalism.
2. 1.2 (of a person) suffer from adverse physiological effects after ingesting, breathing, or touching a substance.
   （人咽下、吸入或触及东西时）产生不良生理反应
   many babies react to soy-based formulas

   许多婴儿对以大豆为主的配方奶粉有不良反应。

   Example sentencesExamples

   • Our findings indicate that children at risk for atopy react sensitively to chemical substances that originate from passive smoking.
   • Why do some members of a family react to environmental substances and develop asthma, while others do not?
   • Therefore you can suddenly react to a substance you may have come in contact with many times before.
   • Those who react to airborne allergens usually have allergic rhinitis and/or allergic conjunctivitis.
   • One of the hardest questions for parents of a young child to answer is whether to have them further immunized when he or she has reacted to a vaccination in the past.
3. 1.3Chemistry Physics Interact and undergo a chemical or physical change.
   〔化，物理〕起化学作用；反应
   the sulfur in the coal reacts with the limestone during combustion

   煤炭中的硫磺燃烧时与石灰石起化学反应。

   Example sentencesExamples

   • Thus, it is unsurprising that rubisco still reacts with both oxygen and carbon dioxide.
   • When base is added, it reacts with hydronium ion to decrease its concentration, thereby stressing the system.
   • Direct sensing mechanisms might involve proteins or ligands that bind or react with oxygen.
   • At higher temperatures, magnesium reacts vigorously with oxygen to produce a blinding white light.
   • In these reactions the ozone reacts with nitric oxide to produce nitrogen dioxide.
4. 1.4Chemistry with object Cause (a substance) to undergo a change by interacting with another substance.
   〔化〕使（物质）起化学反应
   Example sentencesExamples

   • These materials are reacted with sulfuric acid, then neutralized, and converted to a salt.
   • Organic sulfates are esters and are formed by reacting an alcohol with cold sulfuric acid or by the reaction of sulfuric acid with a double bond in an alkene.
   • Many alkyl halides, alcohols, or alkenes can be reacted with benzene in the presence of certain catalysts to give an alkyl benzene.
   • Chloroform can be made from ethanol by reacting the ethanol with calcium hypochlorite.
   • It is made into MSG by reacting the glutamic acid crystals with sodium hydroxide.
5. 1.5Stock Market (of stock prices) fall or rise in reaction to events, developments, etc.
   Example sentencesExamples

   • Just how will bond markets and stock markets react to the anticipated rise in US interest rates?
   • The market reacted positively to the news, pushing BHP's price up 1.5 per cent, to $17.42.
   • Edging down a bit from record highs, but maybe not for long, oil prices react to events in Iraq.
   • The stock price is reacting, up some 50 percent to $15 a share since Payne took charge.
   • The market reacted badly to the news and sent the shares 17 % lower.