In an experiment to see if having a nurse come three times to visit the homes of newborn babies reduces doctor visits, what is the independent variable?

In a research, the independent variable is the one which causes a change in the dependent variable. In this case, the nurse visit in hoped to cause reduction of doctor visits. That means the doctor visit is dependent variable and nurse visit will be the independent variable.

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.