Which one of the following has largest number of isomers ? <br> (R - =alkyl group, en = ethylenediamine )

Question

( A ) $[Ru(NH_3)_4Cl_2^+]$
( B ) $Co(NH_3)_5Cl]^{2+}$
( C ) $[Co(en)_2Cl_2]^+$
( D ) $[Ir(PR_3)_2H(CO)]^{2+}$