Well I think it's gonna be C - 90° N and 90<span>° S - because those latitudes are located exactly on both north and south poles and there's nothing more likely to see glaciers than the poles themselves.</span>
I think it refers to worldwide mutual dependence between nations/countries as we depend on each other for the key things like food etc. on a worldwide level.
I think the two sources would be drip irrigation which is like a river, lake, groundwater, etc... The second source could be is making a new irragation system that could deliver water faster.