Which is on part of the immune system that helps protect the body from diseases?

The B lymphocytes (or B-cells) create antibodies and alert the T lymphocytes (or T-cells) to kill the pathogens. White blood cells are a part of the lymphatic system, a network of lymph vessels that collect excess fluids from tissues throughout the body and then return  to your bloodstream.

Explanation:

answer; (b) medicare fee schedule;

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