Determine whether a relation r on the set of all people is reflexive, symmetric, antisymmetric, and/or transitive, for the following 4 different r's : a) a, b∈r iff a is taller than b b) a, b∈r iff a and b were born on the same day c) a, b∈r iff a has the same first name as b d) a, b∈r iff a and b have a common grandparent