调度指令分分几种？
参考答案：
调度指令分逐项指令、综合指令和即时指令。
She devoted much of her time to ______ the environment.[ ]
A. protect
B. protecting
C. protected
D. protects
My book was here a second ago but now it's missing. Someone ________ a joke on me.[ ]
A. must be playing
B. must play
C. can't have played
D. can't play
