In (a) all the ratios are different so there are no twins or triplets.
In (b) there are only five ratios.
In (c) there are 4 distinct ratios, implying 2 pairs of twins and 2 other children who are not twins.
In (d) there are 4 distinct ratios, implying 1 set of triplets and 3 children who are neither twins nor triplets.
In (e) there are 2 distinct ratios, implying 2 sets of triplets and no other children.