The correct answer is C. Thyroid dysfunction. A goiter refers to the enlargement of the thyroid gland, which can be caused by various thyroid disorders, such as: - Hypothyroidism (underactive thyroid) - Hyperthyroidism (overactive thyroid) - Iodine deficiency - Thyroiditis (inflammation of the thyroid) Goiter is most commonly associated with thyroid dysfunction, where the gland becomes enlarged due to an imbalance in thyroid hormone production or other thyroid-related issues.