Task: Question Answering
Input (English): Question: The term DOMAIN refers to: 
 Options:  <1> The ends of the polypeptide chains of a protein. <2> Compact segments of globular proteins, which are structurally independent and have specific functions. <3> Combinations of alpha helices and beta sheets without a particular function. <4> Each of the individual polypeptide chains of an oligomer. <5> The structure of fibrous proteins.
Output (English): 2