PLEASE HELP

Which phrase best completes the diagram?

***picture shows a diagram with "advantages of the north" in the middle with three words pertaining to that statement which say, "more industrial capacity, larger population, and greater supply of natural resources." ***

A) Better transportation systems

B) More experienced commanders

C) Greater commitment to the cause

D) Strong support of the civilian population

I think it's A and I know that it's not B or C...