If A = \( \left [ \begin{matrix} 1 & 2 \\ a & b \end{matrix} \right ] \) A² = \( \left [ \begin{matrix} 0 & 0 \\ 0 & 0 \end{matrix} \right ] \) then the values of a and b are:

A 2 and 1

B -2 and -1

C -1/2 and -1