Mosquitoes as vectors in malaria transmission Steps:

• Identify key terms for disease transmission roles: vector (transmits pathogen), reservoir (maintains pathogen), intermediate host (supports pathogen development).
• Recall malaria biology: Anopheles mosquitoes biologically transmit Plasmodium parasite by injecting sporozoites during bites, not as hosts or reservoirs.
• Evaluate terms: Only "vector" accurately describes the mosquito's role; humans are reservoirs, mosquitoes are not intermediate hosts.
• Select option matching only the correct term (3).

Why D is correct:

• Mosquitoes are defined as biological vectors in epidemiology, carrying and transmitting Plasmodium from human to human via infected saliva.

Why the others are wrong:

• A includes all, but 1 and 2 (likely reservoir/host) misapply to mosquitoes.
• B includes 1 and 2, ignoring that only vector fits.
• C includes 1, wrongly pairing with vector.

Not enough information on exact terms 1-3, but D aligns with standard biology.

Final answer: D