The matrix below marks with a 1 each pair of the set of racers a, b, c, d, e, f who are to have a drag race together. it is most efficient if a racer can run in two races in a row (but not in three in a row). is it possible to design a sequence of races such that one of the racers in each race (except the last race) also runs in the following race (but not three in a row)? if possible, give the sequences of races (pairs of racers); if not, explain why not.