Identify the compulsion in the following example. Demarco can't stop thinking about his book collection, which includes hundreds of first editions. He wants it to be in a particular order. He spends hours every day organizing his books alphabetically by author, then by color, then by size.

A. thinking about the order of the books all the time
B. thinking about the books all the time
C. having hundreds of first editions in his book collection
D. organizing the books