c. The abnormality is in the thyroid gland itself.
Explanation:
Primary hypothyroidism arises from a pathology in the thyroid gland itself and occurs when the thyroid gland is not able to perform one of its many physiology. Secondary hypothyroidism starts at the level of the pituitary gland and results from under secretion of TSH. TSH is needed to trigger the release of the T3 and T4 stored in the thyroid gland. Tertiary hypothyroidism is caused by a decrease level of the TRH from the hypothalamus. This reduced level, in turn, reduces TSH and thyroid hormone levels in the blood, hence in the body and the patient suffer the symptoms.
