18. There are two uniform dice, each face of the dice is marked with the numbers $1$, $2$, $3$, $5$, $7$, and 8. Now, if these two dice are thrown simultaneously, the probability that the sum of these two numbers is even is ( ).
(A) $\frac{4}{9}$
(B) $\frac{1}{2}$
(C) $\frac{5}{9}$
(D) $\frac{3}{5}$
(E) $\frac{2}{3}$
18. C.

Note that,
the probability of both dice being even is $\frac{2}{6} \times \frac{2}{6}=\frac{1}{9}$, and the probability of both dice being odd is $\frac{4}{6} \times \frac{4}{6}=\frac{4}{9}$. Therefore, the probability that the sum of the two dice is even is $\frac{1}{9}+\frac{4}{9}=\frac{5}{9}$.