If the area bounded between $X$ -axis and the graph of $y=6 x-3 x^{2}$ between the ordinates $x=1$ and $x=a$ is 19 sq units, then ' $a$ ' can take the value
(a) 4 or $-2$
(b) two values are in $(2,3)$ and one in $(-1,0)$
(c) two values one in $(3,4)$ and one in $(-2,-1)$
(d) None of the above