根据所给句子，选择最佳的应答语。每个选项只能用一次。

( )1. Why are you late for class?

( )2. If you don't get enough sleep, you'll be exhausted in class.

( )3. Have you ever been an April Fool, Maria?

( )4. Hi, Michael. You look stressed out today.

( )5. By the time I was five, I had started learning English.

上下颌双侧后牙缺失，排牙时应以哪个关系位置作标准（）。

A.第一双尖牙

B.第二双尖牙

C.第一磨牙

D.第二磨牙

E.第三磨牙