One may conclude that poetic conventions were being challenged by the 1850's from:

Asales data of music publishers from 1820 to 1860.
Bsales data of American publishers from 1820 to 1860.
Cattending a dedication ceremony of a public monument in the 1850's.
Dattending symphonic concerts in the 1850's.
Ean analysis of "Out of the Cradle Endlessly Rocking."

Verified Answer :

The correct answer for the question that is being presented above is this one: "(C) attending a dedication ceremony of a public monument in the 1850's." One may conclude that poetic conventions were being challenged by the 1850's from: attending a dedication ceremony of a public monument in the 1850's.