This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
Which among the following is an early sign of magnesium toxicity? 
Select and explain. 
A. Depression of deep tendon reflexes, B. Respiratory depression, C. Cardia arrest, D. Decreased urine output
A: Depression of deep tendon reflexes
Answer: A: Depression of deep tendon reflexes 
Explanation: Mg toxicity causes muscle weakness. Ref KD Tripati 8th edition