The change in hybridisation of the Al atom in the reaction of $AlCl_3+Cl^-\rightarrow AlCl_4^-$

Question

$\begin{array}{1 1}(a)\;sp^2\;to\;sp^3\;hybridisation\\(b)\; sp^3\;to\;dsp^2\;hybridisation\\(c)\;dsp^2\;to\;sp^3\;hybridisation\\(d)\;\text{there is no change}\end{array}$