A:产生气泡
B:溶液呈蓝色
C:溶液呈紫色
D:产生砖红色沉淀
—I spent two weeks in London last summer.
—Then you must have visited the British Museum during your stay, ________ you?
在一个不透明的口袋中放入除颜色外其余都相同的6个红球和若干个绿球,小颖从中随机摸出一球,记下颜色后,放回,共试验60次,其中记有20个红球,估计袋中有绿球个数为( )