JEE Math Practice Question

Let $$A = \left[ {\begin{matrix} 1 & { - 2} & \alpha \\ \alpha & 2 & { - 1} \\ \end{matrix} } \right]$$ and $$B = \left[ {\begin{matrix} 2 & \alpha \\ { - 1} & 2 \\ 4 & { - 5} \\ \end{matrix} } \right],\,\alpha \in C$$. Then the absolute value of the sum of all values of $$\alpha$$ for which det(AB) = 0 is :

1. A.3
2. B.4
3. C.2
4. D.5