What are four main types of animal tissues Muscular
Support
Epidermal
Epithelial
Connective
Nervous

Connective tissue, epithelial tissue, muscle tissue, and nervous tissue.

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.

B] nitrogen fixationmight be wrong, so correct me.want extra on your answers? just go on my account and go on questions and answer, or ask in the comments!