Which human dietary molecule makes humans less susceptible to antibiotics that inhibit the bacterial folic acid synthesis pathway?

• A. Vitamin B9 (folic acid) obtained in the diet.
• B. Vitamin C (ascorbic acid) eaten in fruits.
• C. Biotin (vitamin B7) which humans synthesize de novo and therefore are unaffected by folate inhibitors.
• D. Vitamin D synthesized with sunlight exposure on the skin.

Answer: (A)