A certain roller coaster has 3 cars, and a passenger is equally likely to ride in any 1 of the 3 cars each time that passenger rides the roller coaster. If a certain passenger is to ride the roller coaster 3 times, what is the probability that hte passenger will ride in each of the 3 cars?

A) 0 B) 1/9 C) 2/9 D) 1/3 E) 1

Key C 是C31 C21 /C31 C31 C31得出来的吗，想来求证

是这么想的