If D is incapable of running the race and no replacement horse is found; and if the horses that run, finish the race from the first to the last, in the order 1, 2, 4, 6 and 7 (corresponding to the numbers of their jockeys) then which of the following must have finished last in the race?
B
As per the question, jockey 5 has not been assigned any horse and hence E has to be assigned to jockey 4 . So B cannot be assigned to jockeys 2 and 6 as per condition(iii).Also, A or C should be ridden by jockey 1 which leaves us with only one choice wherein B is ridden by jockey 7.Hence option(b).