10. There are five cards in a box, marked with $1$, $2$, $3$, $4$, $5$ respectively. Three cards are drawn without replacement, and the probability that the largest one is 4 is ().
(A) $\frac{1}{10}$
(B) $\frac{1}{5}$
(C) $\frac{3}{10}$
(D) $\frac{2}{5}$
(E) $\frac{1}{2}$
10. C.
$$
P(A)=\frac{\mathrm{C}_{3}^{2}}{\mathrm{C}_{5}^{3}}=\frac{3}{10} \text {. }
$$