Which intervention is most effective in restoring healthy gut flora after antibiotic treatment has caused diarrhea?

Rationale: A. Increasing hydration is important for preventing dehydration but does not restore gut flora. B. Doxycycline is an antibiotic and would worsen disruption of gut microbiota. C. Lactobacillus acidophilus (a probiotic) helps restore normal intestinal flora balance after antibiotic-associated diarrhea. D. Psyllium husk is a fiber supplement that aids in bowel regularity but does not restore microbial balance.