TT1-36

诡异儿

Each signal that a certain ship can make is comprised of 3 different flags hanging vertically in a particular order.  How many unique signals can be made by using 4 different flags?

 

A.      10

B.      12

C.      20

D.     24

E.      36

我选12,答案24. 牛人指导一下.

诡异儿

多谢啦!