[求助]GWD 1-9

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

答案是B,请问是怎么算的呢?谢谢!