24. Let the polynomial $x^{3}-a x^{2}+b x-a$ where $(a, b \in \mathbf{R})$ have all real roots. If $a$ is the smallest positive real number that satisfies this condition, and for this real number $a$, the real number $b$ is uniquely determined, then the value of $b$ is ( ).
(A) 8
(B) 9
(C) 10
(D) 11
(E) 12