请教GWD9-- Math-Q13!

The question is:

How many different 6-letter sequences are there that consist of 1A, 2B's, and 3C's?

A.6   B.60   C.120  D.360   E.720

Thank you in advance!

請參考,建議樓主可先使用搜索功能查找,很多題都討論過了

9-13    http://forum.chasedream.com/dispbbs.asp?boardID=22&ID=60207

B?

p(66)/P(33)/(p22)