This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nerve, Subject name: Physiology
If refractory period of nerve is 1/2500th of a second, what can be the maximum frequency of excitation of the nerve? 
Select and explain. 
A. 100 times/sec, B. 250 times/sec, C. 2000 times/sec, D. 2500 times/sec
D: 2500 times/sec
Answer: D: 2500 times/sec 
Explanation: Refractory period is that time period after the first stimulus during which the nerve is "refractory" to another stimulus. Hence, maximum frequency of excitation can be 2500 times in a second, as each next stimulus can excite the nerve if applied immediately at the end of the refractory period (1/2500th of a second).