Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: Isoprene is: 
 Options:  <1> 2-methyl-1,3-butadiene. <2> 2-methyl-2-butene. <3> 2-methyl-1-butene. <4> 2-ethyl-1,3-butadiene. <5> 2-ethyl-2-butene.
