This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Muscle, Subject name: Physiology
Tetanizing stimulation of the muscle causes a sustained forceful contraction due to: 
Select and explain. 
A. Recruitment phenomenon, B. Failure of Ca++ removal from the sarcoplasm, C. Summation of the stimuli, D. "Beneficial effect"
B: Failure of Ca++ removal from the sarcoplasm
Answer: B: Failure of Ca++ removal from the sarcoplasm 
Explanation: "Tetanizing stimulus" means high-frequency stimulation. When stimuli are applied in quick succession, there is release of Ca++, with each stimulus, from the SR into the sarcoplasm. For the muscle to relax, this Ca++ should be pumped back into the SR, which fails to happen due to the rapid succession of stimuli. The muscle remains in a sustained state of contraction, called as "tetanus".