题干
—I've bought all the food for the party tonight.
—Thank you. Then I _______ go to the supermarket.
A：can't
B：mustn't
C：shouldn't
D：needn't
答案(点此获取答案解析）
D
的固定光滑斜面上，有一用绳子拴着的长木板，木板上站着一只猫。已知木板的质量是猫的质量的2倍。当绳子突然断开时，猫立即沿着板向上跑，以保持其相对斜面的位置不变。则此时木板沿斜面下滑的加速度为 ( )