The correct answer is B) disease.
What Europeans brought with them to the Americas that is considered by many to have made the European conquest and colonization of the Americas possible was diseases.
By the time European conquerors and colonizers arrived in the Americas, the Native American Indian tribes were very healthy and clean people that were not immune to all kind of diseases brought by Europeans such as smallpox, influenza, cholera, typhus, measles, diphtheria, scarlet fever, chickenpox, and malaria. These diseases killed most of the indigenous people in America and facilitated European invasion and conquests.