你有三个包，而我只有一个。

You have three bags and I only have ___one.

今天早上来了四个包裹，但只有一个是给马克的。

Four packages came this morning, but only ___one was for Mark.

涂一面，让它干，然后涂另一面。

Paint ___one side, leave it to dry, and then paint the other.