You did not put the listed nations
One explanation could be the differences in climate (environmental factors). The climate in northern Mexico could support the reproduction of the mosquito species, which is a vector of the dengue virus. Other environmental conditions that influence its endemicity could include living conditions and sanitation. The other possiblity could be that the people in the US have developed immunity for the disease, therefore, are unaffected even when infected by the virus.
Doctors are able to see inside your body without having to cut you open
The real answer is B. Facilitated transport.
If a person requires greater return when risk increases, that person is said to be:
risk averse
