Of the following, which is most susceptible to changes in the epigenome? (A) genes
(B) brain
(C) internal organs
(D) hormones

I think this would be A.

If it's a smaller child or infant, place one on the middle of the chest and on the child's back. (if it is a bigger child with enough room for two, place one on the upper right/your left of the chest, and one on the lower left/your right) the pads should never touch each other. 

A. vitamin c is your answer