翻译句子 :这封信必须在5点前寄出

this letter has to be mailed bofore 5

寄出,发信send out.

The letter must be sent out by 5pm.

说明:by 5:30p.m. 不迟于下午 5:30

不用this,因this特指后成了the.

This letter must be sent bofore 5 o'clock.

This letter MUST be sent out before 5 o'clock!

this letter should be mailed before 5pm

The letter must be off by 5pm.