This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parathyroid and adrenal glands, Subject name: Surgery
Which of the following is true about secondary hyperparathyroidism? 
Select and explain. 
A. Commonly occurs in CRF, B. Related to hyperphosphatemia, C. Patients are generally hypocalcemic, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: SECONDARY HYPERPARATHYROIDISM-MC cause is Chronic renal failure-May occur in hypocalcemia secondary to inadequate calcium or vitamin D intake, or malabsorption.-Related to hyperphosphatemia (and resultant hypocalcemia)-Deficiency of 1,25-dihydroxy vitamin D due to loss of renal tissue-Low calcium intake-Decreased calcium absorption