The human immune system uses a variety of means to defend the body from pathogens. of the lists below, which elements are parts of the human immune system?

a. skin, lymph nodes, white blood cells, and spleen

b. mucous, urine, and kidneys

c. white blood cells and red blood cells

d. skin, neurons, muscle cells, and pancreas

a. skin, lymph nodes, white blood cells, and spleen

Explanation:

The human immune system involves various components and organs which protects the body against the disease causing organisms. Among the given options skin, lymph nodes, white blood cells, and spleen is the correct option. This is due to the following facts:

Skin: It forms the outer covering layer of the human body which prevents the entry of the pathogens inside the body.

Lymph nodes: The lymph nodes are the parts of the lymphatic system. It consists of lymphocytes which fights against disease causing pathogens.

White blood cells: The white blood cells are the cells of the immune system which also fights against invading pathogens.

Spleen: The spleen is the spongy soft organ of the human body. It is located in the upper left part of the abdomen. It filters blood as a part of the immune system. The old blood cells as well as the intruding microbes are degraded inside the spleen this way spleen provides the immunity to the body.

d) center of the mid-ocean ridge

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