A:has graded
B: is graded
C: is being graded
D: is grading
—I want to see Mr. White. We have an appointment.
—I'm sorry, but he is not ________ at the moment, for the meeting hasn't ended.
司机开车上坡前,往往加大油门,以提高汽车的速度,这是为了( )
四边形ABCD中,AD∥BC,∠D=90°,如果再添加一个条件,可以得到四边形ABCD是矩形,那么可以添加的条件是____ (不再添加线或字母,写出一种情况即可)
为了灯泡经久耐用,常向灯泡充的气体是( )