根据对话内容，选择正确的图片。

( ) 1. What's your father?  He's a doctor.

( ) 2. What's your mother?  She's a teacher.

( ) 3. What's your aunt?  She's a driver.

( ) 4. What's your uncle?  He's a player.

当手机距离基站较近时，需要降低发射功率，减少其他用户的干扰；当他远离基站时，需要增加功率，克服路径衰耗。所有手机用户都是以（）为一等级来调整发射功率的。

A.1dbm

B.2dbm

C.4dbm

D.8dbm