One may conclude that poetic conventions were being challenged by the 1850's from:
(A) sales data of music publishers from 1820 to 1860.
(B) sales data of American publishers from 1820 to 1860.
(C) attending a dedication ceremony of a public monument in the 1850's.
(D) attending symphonic concerts in the 1850's.
(E) an analysis of "Out of the Cradle Endlessly Rocking."