For equivalence: reflexive, symmetric, transitive.
A: Adding (c,c) gives {(a,a),(b,b),(c,c)} - reflexive, symmetric, transitive. Valid.
B: Adding (c,c),(a,c),(c,a) - reflexive, symmetric ((a,c),(c,a) both present), transitive (all required pairs exist). Valid.
C and D introduce pairs without their symmetric/transitive closures, so they fail.
Hence A and B only.