35 year old man comes to the physician because of severe midline back pain during the past 4 weeks. he has gained 8kg(18lb) during the past 6 months. visual field testing shows decreased peripheral vision in both eyes. an x-ray of the chest shows compression fractures at t10 and l1. there is a healing left rib fracture posteriorly at t8. imaging studies show a pituitary macroadernoma. the most likely cause of his condition is a tumor producing which of the following hormones?
a. acthb. growth hormonec. luteinizing hormoned. prolactine. thyroid-stimulating hormone.