Answer will be $d)$
As, $\%$ of Doctor $A$ successful for stage III =$\dfrac{78}{80}\times 100=97.5$
For stage IV=$\dfrac{2}{20}\times100=10$
As, $\%$ of Doctor $B$ successful for stage III =$\dfrac{49}{50}\times 100=98$
For stage IV=$\dfrac{11}{50}\times100=22$
In both cases Doc $B$ is more successful.