生态农业是一种积极采用生态友好方法，全面发挥农业生态系统服务功能，促进农业可持续发展的农业方式。()

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.