他继续解释他的理论，父母们将会有更多孩子当婴儿死亡率是高的，以便确保若干孩子将能生存下来去照顾他们当他们变老了。

He continued by explaining the theory that parents will have more children when infant mortality is high, so as to ensure that several children will survive to take care of them as they grow old.

youdao

当父母变老了，照顾他们是我的责任。

When my parents are old, it is my duty to take care of them.

youdao

当孩子们长大时，父母们便老了。

When the children grow up, the parents grow old.

youdao