This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, 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. Cardiac arrest, D. Decreased urine output
A: Depression of deep tendon reflexes
Answer: A: Depression of deep tendon reflexes 
Explanation: None