Acidic pH of urine and vaginal secretions inhibits microbial growth.

• A. Tears and saliva
• B. Blood plasma
• C. Urine and vaginal secretions
• D. Cerebrospinal fluid

Answer: (C)

Acidic environments slow or stop many microorganisms, serving as a natural barrier to infection. In the vagina, lactobacilli keep the secretions acidic by producing lactic acid, which helps suppress pathogens. Urine tends to be somewhat acidic as it passes through the urinary tract, adding another chemical barrier to microbial growth. The other fluids—tears, saliva, blood plasma, and cerebrospinal fluid—are typically near neutral pH and rely more on enzymes and immune factors for antimicrobial defense rather than acidity. So recognizing that urine and vaginal secretions provide an acidic environment that inhibits microbes makes this statement the best fit.