What gland secretes thyroid hormone?

The thyroid gland makes three hormones that it releases or secretes into the bloodstream. Two of these hormones, called thyroxine and triiodothyronine , increase your body's metabolic rate. Essentially, the body's metabolic rate is how quickly the cells in your body use the energy stored within them.

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Explanation:

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."