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
During skeletal muscle contraction: 
Select and explain. 
A. A band shorten, B. Both H and I band shorten, C. Both A and I band shorten, D. Both A and H band shorten
B: Both H and I band shorten
Answer: B: Both H and I band shorten 
Explanation: During  muscle contraction,  two Z lines come  closer;  the  length  of  the  ‘A  band’ remains constant whereas the length of H and I band decreases. The M line becomes more prominent.