This question is based on Simpson's Paradox.
1.Success rate of Dr.B in Stage Ⅲ (49/50 =98%) > Success rate of Dr.A in Stage Ⅲ(78/80 = 97.5%)
2.Success rate of Dr.B in Stage Ⅳ (11/50 = 22%) > Success rate of Dr.A in Stage Ⅳ(2/20 =10%)
3.The aggregate Success rate of Dr.B (60%)< The aggregate Success rate of Dr.A (80%)
I recommend Dr. B because her success rate in both stages Ⅲ and Ⅳ is greater than Dr. A.Individual success rate is matter rather than aggregate.
Correct ans is (d)Doctor B since she appears to be more successful