题目

New Year and Its Celebrations（新年习俗） January 1,the beginning of a New Year. As far back in history as we can tell ,people have celebrated（庆祝）the start of a New Year .The people of ancient Egypt began their New Year in summer .That is when the Nile River flooded its banks bringing water and fertility（肥沃）to the land .The people of ancient Babylon（巴比伦）and Persia（波斯）began their New Year on March 21,the first day of spring .And some native American Indians（美洲土著印第安人）began their New Year when the nuts of the oak（橡木）tree be如图所示，A、B球的质量相等，弹簧的质量不计，倾角为θ的斜面光滑，系统静止时，弹簧与细线均平行于斜面，在细线被烧断的瞬间，下列说法正确的是A．两个小球的瞬时加速度均沿斜面向下，大小均为gsinθB．B球的受力情况未变，瞬时加速度为零C．A球的瞬时加速度沿斜面向下，大小为2gsinθD．弹簧有收缩的趋势，B球的瞬时加速度向上，A球的瞬时加速度向下，瞬时加速度都不为零