There is a choice of 7 for the first selected thing, a choice of 6 for the second and a choice of 5 for the third, giving us 7×6×5 permutations. But we could have picked the same three things in a different order, which means the permutations contain duplicate combinations. The duplication factor is given by the number of ways of arranging 3 things=6, so we need to divide 7×6×5 by 6, so there are 35 distinct combinations, answer D.