- A Antibodies circulating in the blood plasma
- B Skin and mucous membranes
- C T lymphocytes patrolling the lymphatic system
- D Fever raising the body's core temperature
Correct answer: B. Skin and mucous membranes
Explanation: The first line of defence includes physical and chemical barriers: skin (prevents entry), mucus (traps pathogens), cilia (sweep pathogens out), saliva, tears (contain lysozyme), and stomach acid.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.