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A goiter is an enlargement of the thyroid in the neck. This can occur due to a deficiency of iodine. Iodine is necessary for the thyroid gland to produce thyroxine ($\text{T}_4$) and triiodothyronine ($\text{T}_3$), hormones used to maintain proper metabolism.

Which of the following explains why the thyroid would be enlarged due to an iodine deficiency?


The thyroid is being continuously stimulated due to a positive feedback loop, causing it to enlarge.


The anterior pituitary is producing too much thyroid-stimulating hormone (TSH), triggering the thyroid to produce more thyroxine ($\text{T}_4$) and triiodothyronine ($\text{T}_3$).


The target cells are not adequately using the thyroxine ($\text{T}_4$) and the triiodothyronine ($\text{T}_3$), causing an accumulation of these hormones in the thyroid.


The thyroid is unable to produce thyroxine ($\text{T}_4$) and triiodothyronine ($\text{T}_3$), which normally inhibit the continued production of thyroid-stimulating hormone (TSH) by the anterior pituitary, so the thyroid is continuously stimulated to produce $\text{T}_4$ and $\text{T}_3$.

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