trying to select every other 1st column, of 2 columns sets.
20 columns, 10 sets. only use one at a time for formula trying to make.
using fixed cell $C$2 to enter 1-10. (first col is a low number, 2nd col is
hi).
selecting 1 column at a time works for the following example.

=INDEX(E49:X9,1,$C$2)

but for example, need 2 to select column G, 3 column I ..
do I need use of / get help with MOD() ?
thanks.