I just want to know. Please tell me, how much do you make an hour? —If you_____ know, I make $20.00 an hour.[ ]

The WHO has given some advice on to prevent us being infected(感染)with H7N9.

With everyone’s face_________behind the mask, it’s hard to tell who they really are.

______ about the missing Beijing-bound Malaysian flight that he decided to look for more information about it.

下列词语中加点的字，每对读音都不相同的一组是