1. Four twenty-five cent stamps, please.
请给我4张25分的邮票。
还能这样说：
I want to buy four twenty-five cent stamps, please.
I'd like four twenty-five cent stamps, please.
应用解析：
bear the stamp of 带……标记；具有……迹象；
stamp down 镇压，践踏；
stamp sth. on 在……上盖印，留下印记；惩治
2. Can you help me mail this letter?
你能帮我寄这封信吗？
还能这样说：
Would you do me a favor to mail the letter?
Could you be kind to post the letter for me?
应用解析：
mailing list 邮寄名单；
mail order 邮购制度；
mails hot （寄给潜在客户的）广告材料；
the mailed fist 威胁，武力威胁
3. I want to post this letter.
我想寄这封信。
还能这样说：
I have a letter to post.
I have a letter to mail.
应用解析：
keep sb. posted 使某人不断获悉最新发展情况或消息等；
post-haste 火速的，赶紧；
post process 后期处理
4. I want this letter registered.
我想寄挂号信。
还能这样说：
By registered letter, please.
I prefer to have the letter registered.
应用解析：
by letter 以书信形式；
call letters （电台）呼号；
in letter and in spirit 无论形式和实际；
claim letter 索赔书