因为我们不确定海星数量增加的原因，所以要预防就很难了。

Bcause we aren't sure of the causes for starfish population increases, it's difficult to prevent them.

youdao

你需要确定蜘蛛的数量。

You have to know the number of spiders.

youdao

为了建立这样一个年表，有必要确定地球过去不同时期存在的陆冰的相对数量。

To establish such a chronology, it is necessary to determine the relative amounts of land ice that existed at various times in the Earth's past.

youdao