Question

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Explanation:

To solve the multiple - choice question about what triggers tumor formation in cancer, we analyze each option:

• Option A: A parasite living and reproducing in the human body may cause various health issues, but it does not directly lead to uncontrolled cell growth which is the main cause of tumors. Parasitic infections typically cause immune responses and damage to tissues in other ways, not by altering the cell cycle for uncontrolled growth.
• Option B: Genes that code for proteins regulating cell division are crucial for normal cell growth and division. A mutation in such a gene can disrupt the normal regulation, leading to uncontrolled cell growth, which is a characteristic of tumor formation.
• Option C: A change in a gene related to skin coloration affects the pigmentation of the skin and has no relation to the regulation of cell division. So, it cannot trigger tumor formation.
• Option D: A bacterial infection causing inflammation and swelling in body tissues is an immune response - related issue and does not involve the alteration of the cell cycle for uncontrolled cell growth, so it cannot trigger tumor formation.

Answer:

B. A mutation in a gene that codes for a protein regulating cell division.