"Which of these relations on the set of all people are equivalence relations? Determine the properties of an equivalence relation that the others lack.
a) {(a, b) ⎢ a and b are the same age}
b) {(a, b) ⎢ a and b have the same parents}
c) {(a, b) ⎢ a and b share a common parent}
d) {(a, b) ⎢ a and b have met}
e) {(a, b) ⎢ a and b speak a common language}"