A car has three carriages, and passengers can take any carriage. The probability of passengers riding three times, only once per car ()

There are three possibilities for each ride, and the total possibility is 3×3×3=27.

And the possibility of taking only three cars is C.

Therefore, the probability P=6/27=2/9.

Answer: H.

30、

There are 8 books on the shelf, of which 2 are soft and 6 are hard. Choose 4 books, at least 1 book, and the choice of soft side is ().

① Only 1 Soft surface: C.

② Two soft faces: C.

So the total * * * is 40+ 15=55.

-Answer: D