某日历上一竖列的相邻三个数的和为63,则中间一个的日期是( )。
21
补全对话。
A: I want _____________ put this table _____________ there. But it's _____________ heavy.
Could you _____________ me?
B: _____________! _____________ do you want to put it?
A: Under the tree.
B: _____________.
A: Please _____________ a bottle of orange.
B: _____________ you.
A: Would you like another one?
B: No. _____________.
一架飞机水平匀速地在某同学头顶上飞过,当他听到飞机的发动机声从头顶正上方传来时,发现飞机在他前上方约与地面成60°角的方向上,据此可估算出此飞机的速度约为声速的多少倍?