Task: Question Answering
Input (English): Question: In relation to the structure of proteins: 
 Options:  <1> All globular proteins have the same domains. <2> The tertiary structure is present only in oligomeric proteins. <3> Hemoglobin is the only protein that has a quaternary structure. <4> The protein domains are regions of compact folding that exert a certain function. <5> The tertiary and quaternary structures are maintained only by the peptide bonds.
Output (English): 4