题目

 The airhostess asked all the passengers on board to remain _______ as the plane was making a landing.    A. to be seating         B. seated             C. seating            D. seat 答案：B如图，若要让反射光线照中目标，在激光笔不动的情况下，可将平面镜（　　）A.竖直向上移动B.竖直向下移动C.水平向右移动D.水平向左移动