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: Cyclopentadiene is so reactive that leaving it at room temperature slowly dimerizes by a reaction of: 
 Options:  <1> Friedel-Crafts. <2> Diels-Alder. <3> Markovnikov. <4> Suzuki <5> Gabriel.
