题目

This March is a busy month in Shanghai．There's a lot to do．Here are the highlights.     Live Music - Late Night Jazz     Enjoy real American jazz from Herbie Davis, the famous trumpet player．He's coming with his new 7-piece band, Herbie’s Heroes．Herbie is known to play well into the early hours, so don't expect to get much sleep．This is Herbie’s third visit to Shanghai．The first two were sold out, so get your tickets quickly.     PLACE: The Jazz Club    DATES: 15---23 March     PRICE: ￥80,120        TIME: 10:00p.m．till late!     TEL: 6413．质量分别为M和m的物块形状大小均相同，将它们通过轻绳和光滑定滑轮连接，如图甲所示，绳子在各处均平行于倾角为α的斜面，M恰好能静止在斜面上，不考虑M、m与斜面之间的摩擦．若互换两物块位置，按图乙放置，然后释放M，斜面仍保持静止．则下列说法正确的是（　　）A．轻绳的拉力等于MgB．轻绳的拉力等于mgC．M运动加速度大小为（1-sinα）gD．M运动加速度大小为$\frac{M-m}{M}$