What makes the United States a heterogeneous country?
A. its diverse population
B. the current white majority of the population
C. its size
D. its democratic vision
"heterogenous" means having variety, not being of the same kind - it is contrasted wth "homogenous" - that is, being very similar, without much variation.
Therefore what makes United States so heterogenous is its diversity - the correct answer is A. its diverse population.
