A:收缩/舒张
B:收缩/收缩
C:舒张/收缩
D:舒张/舒张
有30张牌,牌面朝下,每次抽出一张记下花色再放回,洗牌后再抽,经历多次试验后,记录抽到红桃的频率为20%,则红桃大约有____ 张.
To make a beautiful campus, please ____ ____that rubbish is thrown into dustbins.
圆C1:x-12+y+22=16与圆C2:x-22+y2=1的位置关系是( )