Older People's Particular Susceptibility to STIs Is Exacerbated by Which

Older people's particular susceptibility to STIs is exacerbated by which of the following situations?

A) The immune system is weaker and less effective in elder populations.
B) Older people are less likely to use a condom during sex.
C) Older people are not perceived as being at risk for STIs so they are less likely to be screened by a health care provider.
D) All of the above.