Answer:
A. have subjects wear the shoes in an experimental trial to see if symptoms improve.
Dobereiner could find only three triads; . i.e total of 9 elements only. However the total number of elements were more than that of those encompassed in Dobereiner's Triad. Thus, Dobereiner's could not be classify most of the elements known at that time
That looks like helium
since it has 2 protrons, neutrons, and electrons.