蜜蜂采蜜归来,发出声音的音调变低.原因是负重增加的情况下,蜜蜂翅膀扇动的频率( )
A:变高
B:变低
C:不变
D:无法判断
Please post this letter in the post office nearby, and __________, I will get two tickets in the train station. ( )
写出下面各百分数.
已知两圆的半径分别是4cm和6cm,圆心距是7cm,则这两圆的位置关系是 ( )