This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Myocardial Infarction, Subject name: Pathology
Which of the following causes 'no-reflow' phenomenon in acute myocardial infarction contributing to reperfusion injury? 
Select and explain. 
A. Myocyte hypercontracture:, B. Leucocyte aggregation, C. Free radicals, D. Complement activation
B: Leucocyte aggregation
Answer: B: Leucocyte aggregation 
Explanation: Factors that contribute to reperfusion injury in myocardial infarction include the following: Mitochondrial dysfunction Myocyte hypercontracture Free radicals Platelet and complement activation Leukocyte aggregation - may occlude the microvasculature and contribute to the "no-reflow" phenomenon.