I'm trying my best, but I just can't do it.

我在尽最大努力 可就是做不来

D try one's best to do sth.

“尽某人的最大努力做某事”，是固定短语。

Try one's best to do sth.

要尽力去做某件事情的意思。

Must try one's best to serve the people.

一个人要尽全力来为人民服务。

Try one's best is a necessary personality.

全力以赴，是一种必要的品格。

A lot of people utilize this chance to try one's best to purchase, in order to leave some stocks.

许多人利用这个机会尽量采购，以便留些存货。