包外壳

例句：

1. 1.The letter was enclosed in an envelope.
   这封信被一个信封包裹着。
2. 2.She carefully wrapped her gift in an envelope.
   她小心翼翼地用一个信封包装了她的礼物。
3. 3.Please send the parcel by registered mail to ensure it arrives safely.
   请通过挂号邮件发送这个包裹，以确保它安全到达。