Assume each variable has a different value. which relations below are functions? a. {(a, b), (a, c), (a, d), (a, e)} b. {(a, b), (b, b), (c, b), (d, b)} c. {(a, b), (c, d), (e, f), (g, h)} d. {(a, a), (b, c), (c, c), (d, e)}

a. choice a only

b. choices b and c only

c. choice c only

d. choices b, c, d only