题干
---You’re going to collect money for the drought areas in southwestern China?
---______. We should try our best to give them a hand.
A：No, I am not
B：No, I was just joking
C：Yes, I do
D：Yes, I have never been more seriou
答案(点此获取答案解析）
D
5kg的小环B，它与杆之间有摩擦。若环从底座上以v0=4m/s的速度飞起，刚好能到达杆顶（g=10m/s2）。下列说法错误的是 （ ）
