19. In a jar, there are red, green, and blue balls. It is known that there are 6 balls other than the red ones; 8 balls other than the green ones; and 4 balls other than the blue ones. Then the total number of balls in the jar is (   ).
(A) 6
(B) 8
(C) 9
(D) 10
(E) 12
19. C.

Let the number of red, green, and blue balls be $x$, $y$, and $z$ respectively. According to the problem, we have
$$
\left\{\begin{array}{l}
y+z=6, \\
z+x=8, \\
x+y=4 .
\end{array}\right.
$$

Solving these equations, we get $x+y+z=9$.