Task: Question Answering
Input (English): 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.
Output (English): 1