名词
中文翻译：收缩
同义词：
['shortening', 'shortening process', 'shortening effect']
例句：
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1. The muscle contracted as the person lifted his arm.
当这个人抬起他的手臂时，肌肉收缩了。
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2. The muscles in your arms are contracting to help you lift your arms.
你的手臂里的肌肉正在收缩，帮助你抬起手臂。
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3. During exercise, the muscles in your legs are contracting to increase your speed.
在运动中，你腿部的肌肉正在收缩，以增加你的速度。