图中“O，这是闭合电路的一部分，它在磁场中的运动方向如图所示，不可能产生感应电流的是[ ]
A.
B.
C.
D.
答案：C
Almost all of his time ______ experiments, he has no time to visit his parents.
A．devoted to do
B．devoted to doing
C．devoting to doing
D．is devoted to doing
下列混合气体，点燃会发生爆炸的是（ ）
A．H2和CO
B．CO和CO2
C．N2和H2
D．CH4和空气
