—Where is your PE teacher?          

—Look! Our PE teacher is swimming. He            swimming for exercise.             [ ]

A. can't be                

B. might              

C. must be

在打印机工作进行时，需中断目前的打印，可按（）键，缺纸灯熄？

A.换页

B.联机

C.ONLINE

D.断开