A、同工酶
B、变构酶
C、米氏酶
D、丙酮酸脱氢酶系
If the firm' s average cost curves are U-shaped, why does its average variable cost curve achieve its minimum at a lower level of output than the average total cost curve?
A.S形
B.波形
C.弧形
D.圆形
一物体沿曲线为r=2θ的轨迹运动,如果角度θ=t2,求θ=π/2时物体运动的速度v、加速度a的大小(t表示时间).