放入封套

例句：

1. 1. Please put the letter in the envelope and mail it to me.
   请把信放进信封并寄给我。
2. 2. The postman delivered a package in an envelope.
   邮递员在一个信封里投递了一个包裹。
3. 3. She carefully placed the documents inside the envelope.
   她小心翼翼地将文件放在信封里。