题目

Every possible means ______to prevent the air pollution, but the sky is still not clear.    A. is used      B. are used     C. have been used          D. has been used 答案：D1．如图所示，A为固定的斜面体，其倾角为θ=30°，B为固定在斜面下端与斜面垂直的木板，P为动滑轮，Q为定滑轮，两物体的质量m1=0.4kg，m2=0.2kg，斜面的绳子与斜面平行，绳不可伸长，绳、滑轮的质量及摩擦不计，求m2的加速度及各段绳上的张力．