If Jockey 5 is the one not assigned to any horse, which of the following could be true?
F is ridden by Jockey 6
If Jockey 5 has not been assigned any horse,then E is ridden by jockey 4.Consequently,from condition(iii),B cannot be ridden by Jockey 6.As per condition(iv), we cannot have jockey 7 riding C.So options(a),(c) and (d) are eliminated.