原因是其母亲身体不行了，走路困难，坐下都站不起了，比一般的同龄老人身体差。

This is because her mother Lin is not well and has difficulty walking. Lin cannot stands up after she sits down. Her health is much worse than the average person for her age.

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他们发现他身体半裸，流着血，快不行了。

They found him half naked and bleeding to death.

《牛津词典》

当然，有许多疾病让身体付出了代价，损坏了身体，不管这人以后有多么健壮矍铄，多么乐观开朗和热情，身体就是不行了。

There are, of course, many illnesses that take a toll on the body, damage the body, and no matter how hale the person might be later, how optimistic and enthused, the body simply is not able.

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