Instructions: In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.
Input: Question: In neurons once an action potential has started, a second action potential can not be triggered for a short period of time, regardless of the intensity of the stimulus applied. This period of time is known as:
Options: <0> Synaptic delay. <1> Threshold depolarizing period. <2> Absolute refractory period. <3> Relative refractory period. <4> Spatial sumary.
Output:
nursery