A:that
B:whether
C:if
D:whe
写出下列单词的过去式。
( 1 )sleep____ ( 2 )have____
( 3 )read____ ( 4 )watch____
( 5 )drink____ ( 6 )stay____
( 7 )wash____ ( 8 )play____
( 9 )clean____ ( 10 )do____
如图所示,一束激光AO由空气斜射入玻璃砖,折射后从另一侧面射出,其出射光的出射点可能是图中的( )
直角坐标平面内,一点光源位于A(0,5)处,线段CD⊥x轴,D为垂足,C(3,1),则CD在x轴上的影长为 ____ ,点C的影子的坐标为____ .
When I hear the sound of the ball ____ (hit) the floor, my heart follows its beat.