Simple past tense and past participle of react.(verb)
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Use "reacted" in a sentence
"Note that the first link in this article (the word reacted "reacted") is malformed and does not work (it is possible that it works with some browsers but I doubt)."
"Palin reacted as if Crowley had just sent roses and an ice-cream cake: Happy B'day Ahmadinejad wish sent by US Govt."
"When Chinese people emulated our Boston Tea party and threw British opium into Hong Kong Harbor, Britain reacted by fighting and winning a war against technologically inferior China and then annexing Hong Kong."