请教一道排列组合题

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

是 P（4,4）=24吗？

提醒了我，结果一样，算法应该是P(4,3)

题中前面所说是：每个signal 要由３个不同旗子组成，那么有４个不同旗子时，结果是　从４个中任意取出３个全排列　的个数

就是4 旗子里面取3个排列顺序，VERTICAL是迷惑人的，因为通常排列都是横着排队，垂直排吓人呐

P(4,3)=4!/(4-3)!=4X3X2X1/1=24