Which of the relations below on the set of all people are equivalence relations? Determine the properties of an equivalence relation that the others lack (i. e. not reflexive, not symmetric, etc.) (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}