D would be correct.
"Division of Labor" does not apply to any specific field, it applies to all fields. This rules out A and B.
Work can be split into a variety of different ways, not just two people, and not always equally. This rules out C.
"Division of Labor" can be thought of as an assembly line. 10 people can stand in a row, each adding something to a product going down the chain, until the product is complete. Without all 10 of those people doing their jobs, they would not have the final product.
Then to go even further, that product (say a computer chip) can be sold to another company (say a laptop manufacturer) to develop another entirely different product.
