请教GWD的一道数学题

Q2:

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 the passenger will ride in each of the 3 cars?

                                    A.        0

B.        1/9

C.        2/9

D.       1/3

E.        1

key C

A gardener is going to plant 2 red rosebushes and 2 white rosebushes.  If the gardener is to select each of the bushes at random, one at a time, and plant them in a row, what is the probability that the 2 rosebushes in the middle of the row will be the red rosebushes?

                                    A.      1/12

B.      1/6

C.      1/5

D.     1/3

E.      1/2

Key  B