Which one of the following is expected to exhibit optical isomerism ? (en = ethylenediamine)

Question

( A ) ${cis}-[Pt(NH_3)_2 Cl_2]$
( B ) ${cis}-[Co(en)_2Cl_2]$
( C ) ${trans}-[Co(en)_2Cl_2]$
( D ) ${trans}-[Pt(NH_3)_2Cl_2]$