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: Biochemistry
Substrate affinity to enzyme in Competitive inhibition 
Select and explain. 
A. Decreases, B. Increases, C. Any of the above, D. Does not change
A: Decreases
Answer: A: Decreases 
Explanation: Significance of Km (Michaelis Constant):

Km is substrate concentration at 1/2 Vmax
Constant for an enzyme substrate pair
It is called signature of the enzyme
Higher the Km, lower is the affinity of the enzyme towards the substrate
Lower the Km, higher is the affinity of the enzyme towards the substrate.

Features of competitive inhibition:

Km increases, hence the affinity is lowered
Vmax remains the same.

Features of noncompetitive inhibition:

Km remains the same
Vmax decreases.