This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Circulation: Circulatory Shock and Its Treatment, Subject name: Physiology
First response to decreased blood volume - 
Select and explain. 
A. Increased heart rate, B. Tachypnea, C. Hypotension, D. Disorientation
A: Increased heart rate
Answer: A: Increased heart rate 
Explanation: Ans. is 'a' i.e., Increased heart rate Severity of decreased blood volume