The correct option is B Thyroid gland
Graves' disease is an autoimmune disease. It affects the thyroid, causing it to enlarge to twice its size or more (goitre), become overactive, with related hyperthyroid symptoms, such as increased heartbeat, muscle weakness, disturbed sleep, and irritability. It can also affect the eyes, causing bulging eyes (exophthalmos). It affects other systems of the body, including the skin, heart, circulation and nervous system.