【单选题】The historian Frederick J. Turner wrote in the 1890's that the agrarian discontent that had been developing steadily in the United States since about 1870 had been speeded by the closing of the intern...
A.
a proposal by Frederick J. Turner that was later disputed by John D. Hicks.
B.
an elaboration by John D. Hicks of thesis that formerly had been questioned by Turner.
C.
the thesis that important changes occurred in the nature of international trade during the second half of the 19th century.
D.
the view that the American frontier did not become closed during the 19th century or soon thereafter.