envelope

他正在递出一个信封。

He is handing over an ___envelope.

请把信放进信封里再寄出去。

Please put the letter in the ___envelope before sending it.

我需要一些信封来寄这些文件。

I need some ___envelopes to mail these documents.

我在抽屉里发现了一个信封，上面写着一个地址。

I found an ___envelope with an address written on it in the drawer.