题目

My parents live in a small village. They always keep candles in the house _____ there is a power out.   A. if                             B. unless               C. in case                     D. so that 答案：C一雨滴从空中由静止开始沿竖直方向落下，若雨滴下落过程中所受重力保持不变，且空气对雨滴阻力随其下落速度的增大而增大，则图4所示的图象中可能正确反映雨滴整个下落过程运动情况的是（     ）