—Twice a week.
A:How long
B:How soon
C:How much
D:How often
如图所示的电路图中,电源电压保持不变,闭合开关S后,将滑动变阻器R2的滑片P向左滑动,下列说法正确的是( )
He ________ to escape from the prison,but were stopped by the guards.( )