In the set X = {a,b,c,d} which of the following relations represents a function ?

Options

A. `R_1` = {(b,a),(a,b),(c,d),(a,c)}
B. `R_2` = {(a,d),(d,c),(b,b),(c,c)}
C. `R_3` = {(a,b),(b,c),(c,d),(b,d)}
D. `R_4` = {(a,a),(b,b),(c,c),(a,d)}

Answer

B