Which of the following statements is not true re- garding parathyroid glands and parathyroid ade- nomas?

a. ectopic parathyroid glands account for approxi- mately 15% of the total.
b. the carotid bulb, thymus, retroesophageal, and intrathyroidal regions represent ectopic locations.
c. normal parathyroid glands are never detected by sonography.
d. normal cervical structures such as the longus colli muscle (LCM), esophagus, and small ex- trathyroidal arteries and veins can mimic parathyroid adenomas.