题干
13. ___ had they reached the 30th floor ____ they realized that they had forgotten to take the key.
A：Hardly; tha
B：Hardly; whe
C：No sooner; whe
D：No sooner; the
答案(点此获取答案解析）
B
平抛一个小球1，同时从地面以速度
竖直向上抛出一个小球2，两小球在空中相遇则：( ) 
．(2) 从抛出到相遇所用时间为
(4)．相遇时小球2上升高度
