Translation of "Registered" in Chinese

By registered letter?

寄掛號嗎？

All participants must be registered.

所有的參加者都得註冊。

Please send this by registered mail.

請用掛號寄這個。

I want to have this letter registered.

我想要用掛號寄這封信。

I registered at this school two years ago.

两年前我在这个学校注册了。

What do I have to do now that I'm registered?

我注册了，现在该干什么呢？

You had better get this letter registered for fear it should be lost.

為免丟失，你應該把信件掛號。