According to the Text,why Did Diseases Such as Smallpox and Measles

According to the text,why did diseases such as smallpox and measles produce epidemics that ravaged or completely wiped out native populations in the Americas after contact with Europeans in the late fifteenth century?

A) because Europeans refused to share their medicines with the native peoples
B) because the native peoples lacked resistance to these diseases
C) because Europeans forced the native peoples to relocate to massive urban centers, where the bacteria easily spread
D) because Europeans forced the native peoples to abandon their traditional medicines, which had kept the diseases largely at bay before contact
E) because native peoples fled from their traditional locations before the European onslaught and found themselves without adequate food, medicine, and shelter