Independent variable represent the variable
The answer is D, white blood cells.
The main function of white blood cells is to defense the body from bacteria or other pathogens. There's 2 main kinds of white blood cells, lymphocytes and phagocytes. Lymphocytes mainly produce antibodies that can kill bacteria or any pathogens, and phagocytes can ingest the pathogens directly.
Therefore, since the white blood cells can protect our body, they're part of our immune system.
This is called purging. Purging is a situation when a person gets rid of ingested food <em>voluntarily</em>. This is in contrast to vomiting which is often involuntary. Purging is usually manifested by people with eating disorders such as <em>buliumia nervosa</em> and body dysmorphic syndromes.
<em>Starvation is the lack of nutrients due to reduced intake of food and constipation is reduced frequency of defecation associated with difficulty in defecation.</em>
