我有一个苹果。

I have ___one apple.

我们班只有一个人会弹钢琴。

There's only ___one person in our class who can play the piano.

她是唯一一个能解决这个问题的人。

She's the ___one person who can solve this problem.

我们团结一心，共同面对挑战。

We stand as ___one to face the challenges together.