According to recent studies, if the of the primate brain has a larger than average volume, the more likely that primate is to be sneaky.

I think the blank refers to 80% of the mass.  The theory called Machievellian Intelligence Theory, it states that the larger the brain of a primate the higher social skills it possesses. Aside from the complex skills, it also possesses better cognitive skills compared to other mammals.

answer: - b cells

explanation: -

there are many types of white blood cells present in our body. one such class of white blood cells are the lymphocytes. the b cells belong to the lymphocyte class of wbcs. the b cells perform their action against the pathogen by producing specialised proteins called as antibodies. these antibodies are produced as and when the b cells encounter pathogens in response to the antigens present on the surface of the pathogen. these antibodies bind to the antigens present on the pathogen and then, target them for destruction by other cells of the immune system.

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.