题目

如图所示,，A、B两物体的质量分别为mA和mB，且mA＞mB，整个系统处于静止状态，小滑轮的质量和一切摩擦均不计．如果绳的一端由Q点缓慢地向左移到P点，整个系统重新平衡后，物体A的高度和两滑轮间绳与水平方向的夹角B如何变化    A.物体A的高度升高，θ角变大    B.物体A的高度降低，θ角变小    C.物体A的高度不变，θ角不变     D.物体A的高度升高，θ角不变A disappointing performance Tom was sick with disappointment. The piano performance was almost a success, however, he f  (76)    in his solo(独奏). He couldn’t understand how it could have happened. He had practiced for weeks that seemed like m   (77)  . He had given up sports until after the performance because he wanted to make his parents p  (78)   of him. He spent all his time with the piano. His teacher had said he was q  (79)   to learn. It was true that he accepted music as another l  (80)  , another way to talk to people. His grandparents, aunt, and uncle all came to hear him play, and he was anxious to s  (81)   them that he was the best in the whole class. But, when he stood up to go to the piano, his knees felt w  (82)  . He looked into the audience and saw his f  (83)   smiling back at him. At this time, he felt n  (84)  . His fingers began to tremble (颤抖), shaking as though he had caught a bad cold. He sat down at the piano. He took a deep breath. He played the first part of his music, then realized with fear that he had forgotten the rest. He s  (85)   over, thinking that would help. It didn’t. his bright musical life seemed to end.