Akey reason for the resurgence of measles and mumps infections is a public backlash against vaccinations. an increased mosquito population. poor sanitation and hygiene in certain areas. the rise of the hiv/aids epidemic.

The right answer is: 
Infections is a public backlash against vaccinations.

Measles and mumps are not transmitted by mosquitoes and are not transmitted due to poor sanitation, it is transmitted by the breath. 
Measles and mumps are not contracted due to the weakness of the immune system (nothing to do with HIV/AIDS). it is just a reaction against vaccinations.

Vaccination is a process of introducing an external agent (the vaccine) into a living organism to create a positive immune response against an infectious disease, but not as harmful as a true infection. (This is the key reason for the resurgence of measles and mumps)