Can you solve?

Which of the following relations on (a,b,c,d) is an equivalence relation? Select one: O a (la a), (b.c),(6.b), (cb), (d.d)] O b.((a.a), (b,b), (c.c), (c,d), (cb), (d.d), (d.c)} O cl(a.a),(a,d) (b,b), (b,c). (cc), (c.b), (d,d), (da)) O d. (la,a), (6,5), (b.c), (b,d). (c.c). (cb), (d.d), (d.b)}