If `n, (n > 5)` things are arranged in a circular order, the number of ways of selecting three of the things so that no two of which are next to each other is

If n objects are arrange in a row,then the number of ways of selecting three of these objects so that no two of them are next to each other is a.^(n-2)C_(3) b.^(n-3)C_(2) c.^(n-3)C_(3) d.none of these

If 'n' things are arranged in circular order, then show that the number of ways of selecting four of the things no two of which are consecutive is (n(n-5)(n-6)(n-7))/(4!)

Ten persons are arranged in a row.The number of ways of selecting four persons so that no two persons sitting next to each other are selected is