如果要消耗热量300kcal,自行车运动需要多长时间()
A.20分钟
B.40分钟
C.60分钟
D.80分钟
E.100分钟
参考答案:C
如图电路中,为三个可变电阻,有一带电油滴在平行板电容器两板间静止。要使油滴上升可[ ]
A.减小
B.减小
C.减小3
D.增大
Mary, along with her parents ________ Hainan for a week and they will come back soon.
A.have been to
B.has been in
C.have been in
D.has been to