题目

各个面都光滑的直角三角体 A 放在光滑的斜面 B 上时，恰好使一直角边水平，如图所示，将－个小球置于该光滑直角边水平面上，然后将三角体 A 由静止释放，则小球在碰到斜面之前的运动轨迹是 （ ） A . 平行斜面向下的直线 B . 竖直向下的直线 C . 无规则曲线 D . 垂直斜面的直线 答案：B从方框中选出适当的答语，把字母填在句子前面的括号中. (　　)(1)What were you doing when it rained yesterday? (　　)(2)Are you going to see "Batman"? (　　)(3)Will people live on the moon in the future? (　　)(4)I can't sleep. What should I do? (　　)(5)What will happen if I walk to school? (　　)(6)What did your English teacher say? (　　)(7)If I fail the test, what will my father say? (　　)(8)How many languages can he speak? (　　)(9)My friends didn't invite me to their party. What should I do? (　　)(10)What are you going to wear for Mary's party?