A liquid P, light yellow in colour, circulates in the human body only in one direction (from body tissues to the heart). P contains germs from cells and dead cells. P is cleaned of germs and dead cells by a special type of white blood cells called as

The correct option is B Lymphocytes
The lymph fluid (P) inside the lymph nodes contains lymphocytes, a type of white blood cell, which continuously recirculates through the lymph nodes and the bloodstream. Molecules found on bacteria cell walls or chemical substances secreted from bacteria, called antigens, are taken up by antigen cells into the lymph system and then into lymph nodes. In response to the antigens, the lymphocytes in the lymph node make antibodies which will go out of the lymph node into circulation, target the pathogens producing the antigens by targeting them for destruction by other cells and complement.

Therefore, the correct answer is option A.