Colonies were kind of circular and trapped. They provided the resources and many times could then only purchase manufactured goods from the parent nation. In response to Empr Guy, it hurt nations that did not industrialize. Whereas in the past agricultural economy they would not have lagged so far behind instead they became leaps and bounds behind more industrialized nations.
I would go with B and argue that the British could and did lose to Zulus (Africans). Example being the Battle of Isandlwana. It was rare and is really only noted because it showed that they could win, but in general Europeans stomped any colonies due to technological superiority. A fun note that I always like about that battle was that even though the Zulus absolutely slaughtered the British regulars, they were told to not attack anyone in black because that meant they were civilians and they followed this order (ironically this spared the officers though because of their dark blue uniforms lol)
D is most definitely not the answer. Europe (and more importantly the industrialized parts of Europe) were far outproducing what their own markets demanded. If there had been no foreign markets (their own colonies) to sell to, then Europe would have gone into a deep recession/depression due to overproduction.