In which one of the following species does the transition metal ion have $d^3$ electronic configuration?

Question

$\begin{array}{1 1}(a)\;[Cr(NH_3)_6]^{3+}\\(b)\;[Co(OH_2)_6]^{2+}\\(c)\;[CoF_6]^{3-}\\(d)\;[Fe(CN)_6]^{3-}\end{array}$