They don't have joints and limbs or organs or flesh.

他们没有关节四肢，器官血肉。

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and the ground is really soft, so that you don't end up hurting your joints.

土地也很柔软，这样你的关节就不会受伤了。

What do you 实战 - SpeakingMax英语口语达人

So biomedical engineers have been working for many years on how to design replacement parts for joints like the hip: the artificial hip is the most well developed of those.

因此,生物医学工程师花了很多年时间,致力于设计像髋关节这样的关节替代品,尤以人工髋关节的研究最为成熟

耶鲁公开课 - 生物医学工程探索课程节选