stimulant 与 stimulus 都被译作“刺激物”（见《新英汉辞典》、《远东英汉大辞典》、《牛津现代高级英汉双解辞典》等）。不知这两个词有无区别？
stimulant 本是个医学术语, 主要是指饮料(茶、咖啡、可可、酒等)和药物:
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Tea, coffee, and cocoa are true stimulants to the heart, nervous system and kidneys. （WNDS）茶、咖啡、可可对于心脏、神经系统和肾脏是真正的刺激物。
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Athletes are forbidden to take stimulants before a race. (ELD) 体操运动员禁止在比赛之前服兴奋剂。
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Drugs which speed up cell activity are called stimulants. (WNDS) 加速细胞活动的药物叫做兴奋剂。
stimulus 则是个生理学和心理学术语, 主要是指温度、光、声音、压力等环境的变化对动植物的刺激。
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Light is a stimulus to growth in plants. (LDCE) 光对于植物的生长是一个刺激因素。
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Reduced tariffs were a stimulus to foreign trade. (MD) 关税降低对于外贸是一个刺激因素。
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The good news was a stimulus to all who heard it. (ELD) 这个好消息对于所有听到它的人都是一个鼓舞。
请做下面的英语试题：
In order to adjust to their surroundings, organisms must respond to such stimuli to be light,
temperature, and pressure. (TOEFL)