Anti-malarial drugs target the malaria parasite in human blood

Steps:

• Malaria is caused by Plasmodium parasites transmitted by mosquito bites.
• The parasites enter the bloodstream and multiply inside red blood cells.
• Anti-malarial drugs interfere with parasite metabolism or replication.
• This kills the parasites, reducing infection and symptoms.

Why B is correct:

• Anti-malarial drugs like chloroquine directly kill Plasmodium in the bloodstream by disrupting its ability to detoxify heme, a byproduct of hemoglobin digestion.

Why the others are wrong:

• A: Drugs do not kill mosquitoes; insecticides target vectors.
• C: Drugs do not affect mosquito breeding; that's environmental control.
• D: Drugs act after infection; prevention uses vaccines or repellents.

Final answer: B