Ans. is 'b' i.e., R2 type WHO classification of antimalarial drug resistance 1. S-sensitive --> If a sexual parasites have cleared by day 6 from the begining of treatment wihout subsequent recrudescence until day 28. 2. R1-Low grade resistance --> Recrudescence of infection between 7-28 days of completing treatment. 3. R2 High grade resistance --> Reduction of parasitemia by more than 75% at 48 hours of completing treatment but failure to clear the organism within 7 days. 4. R3-> Parasitemia does not fall by more than 75% within 48 hours of completing treatment and there is no subsequant clearance of asexual parasites.