In which part of the cloaca in birds, bursa of fabricus opens?

Answer: Option B

Bursa of fabricus opens in Proctodeum part of the cloaca in birds.
The bursa of Fabricius is a blind, lymphoepithelial diverticulum of ectodermal origin, located in the dorsal proctodeum of the avian cloaca.
The bursa of Fabricius is the primary lymphoid organ in avian species. The bursa of Fabricius of birds has an essential role as a central lymphoid organ for the differentiation of B lymphocytes. In addition, the bursa harbors immune competent B lymphocytes which are capable of local antibody production.