治疗PD最基本最有效的药物是()
A.抗胆碱能药物
B.金刚烷胺
C.L-Dopa及复方L-Dopa
D.DA受体激动剂
E.MAO和COMT抑制剂
参考答案:C
20. When a stick is partly in a glass of water, it looks ________ it were broken.
A.even though
B.although
C.as if
D.so that
用如图所示滑轮组提升重物.人用250N的拉力F,10s内使重为400N的物体匀速上升了2m.不计绳重和摩擦,求:
(1)动滑轮的重.
(2)人拉绳子做功的功率.
(3)滑轮组的机械效率.