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: Physiology
O2 delivery to tissue is decreased by 
Select and explain. 
A. Decreased haemoglobin level, B. Increased haemoglobin level, C. Increased PaCO2, D. Increased HCO3
A: Decreased haemoglobin level
Answer: A: Decreased haemoglobin level 
Explanation: None