箱子里有大小相同的3种颜色玻璃珠各若干颗，每次从中摸出3颗为一组，问至少要摸出多少组，才能保证至少有2组玻璃珠的颜色组合是一样的？

A.11 

B.15 

C.18 

D.21

Beihai Park is     a beautiful place that      many people come to visit it every day.

A．such; so

B．so; such

C．such; such

D．so; so