Simple goiter is the disease affecting the [D] Thyroid gland. It involves the abnormal enlargement of the thyroid gland, typically due to iodine deficiency, which impairs thyroid hormone synthesis. This condition can lead to a visible swelling in the neck area, causing difficulty swallowing or breathing. Simple goiter does not affect the gums [A], tear gland [B], or liver [C]. Adequate dietary iodine intake is crucial for preventing simple goiter, although other factors such as genetic predisposition or certain medications may also contribute to its development. Treatment may involve iodine supplementation or thyroid hormone replacement therapy.