【单选题】Born in the trough of the Great Depression, Edmund Phelps, a professor at Columbia University who won the Nobel Prize for economics, has spent much of his intellectual life studying slumps of a differ...
A.
unemployment is a hot potato for economists to study.
B.
unemployment is the topic that interests Mr. Phelps the most.
C.
Mr. Phelps's parents asked him to study unemployment.
D.
Mr. Phelps's research is based on the existing research results.