Final answer:
The typical pH range of the skin and vagina, which is part of the first line of defense against microbes, is between 3 and 5, with the acidic environment inhibiting the growth of many pathogens.
Step-by-step explanation:
The typical pH range of the skin is slightly acidic to maintain a microbe-inhibitory environment. This acidic environment is not conducive to many bacteria and fungi that might otherwise thrive on the skin and cause infection. In the vagina, a particularly acidic environment is maintained by the predominant Lactobacillus species, which produce lactic acid and ensure a pH below 4.5.
This inhibits the growth of pathogens and contributes to the vagina's role as a self-cleansing organ. Considering the provided information, the correct answer for the typical pH range of skin and vagina as part of the first line of defense is D. pH 3-5.