5. The following numbers are 4 of the possible sums of the numbers facing up when three dice are rolled simultaneously. Among them, ( ) has the highest probability of appearing in one roll.
(A) 7
(B) 8
(C) 9
(D) 10
5.D.

The probability of getting a sum of 7 is $\frac{15}{6^{3}}$; the probability of getting a sum of 8 is $\frac{21}{6^{3}}$; the probability of getting a sum of 9 is $\frac{25}{6^{3}}$; the probability of getting a sum of 10 is $\frac{27}{6^{3}}$.