只需要几个动作，可以扭转因年龄而自然发生的肌肉损失。
With just a few moves, you can reverse the trend of naturally occurring muscle loss that happens with age.
冲突不会由于群体的差别而自然发生，而是由附着于这些差异本身的特殊意义所致。
Conflict does not arise naturally because of the differences of groups of people but because of special meanings attached to these differences.
人类疾病动物模型在医学研究中起着非常重要的作用，而自然发生的人类疾病已远远不能满足医学研究的需要。
Animal model of human disease plays an important role in medical research, but spontaneous human disease cannot satisfy needs of medical research.
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