—Oh, we won't have supper_______ your dad comes back.
A:until
B:since
C:while
D:after
I know he's been curious about everything, but that's . Be patient!
如图表示一个楼梯,楼梯上面有一个平台。楼梯的斜坡长L=5m,平台高h=4m,平台长s=3m。某人手提质量为25kg的水桶沿楼梯匀速上楼,然后走到平台右端。这一过程中人所做的功是 ____ J。(g取10N/kg)