Which of the following will give a pair of enantiomorphs? (en = $\text{NH}_2\text{CH}_2\text{CH}_2\text{NH}_2$)

A pair of enantiomorphs (optical isomers) exists for chiral complexes that are non-superimposable on their mirror images. This requires the absence of a plane of symmetry. (A) $[\text{Co}(\text{NH}_3)_4\text{Cl}_2]^+$, an $[Ma_4b_2]$ type complex, exhibits geometrical isomerism (cis and trans). Both isomers possess a plane of symmetry and are optically inactive. (B) $[\text{Cr}(\text{NH}_3)_6][\text{Co}(\text{CN})_6]$ consists of highly symmetrical $[Ma_6]$ type complex ions, neither of which shows optical isomerism. (C) $[\text{Co}(\text{en})_2\text{Cl}_2]^+$, an $[M(AA)_2b_2]$ type complex, exists in cis and trans forms. The trans-isomer has a plane of symmetry and is optically inactive. The cis-isomer, however, lacks a plane of symmetry and is optically active, existing as a pair of enantiomers (dextro and laevo). (D) $[\text{Pt}(\text{NH}_3)_4][\text{PtCl}_6]$ contains a square planar cation and an octahedral anion, both of which are highly symmetrical and optically inactive.