Dennis Argues That Lehman (Age and Achievement) May Have Introduced

Dennis argues that Lehman (Age and Achievement) may have introduced bias into his study by ______.

A) using as a criterion for inclusion of a work as a "significant contribution" the appearance of the work in lists of "best" books, "best" operas, and so on
B) assessing the importance of work done over several decades, which assumes that standards of excellence in all fields do not change
C) failing to acknowledge that the number of creative workers in all fields has greatly increased, thereby substantially increasing the competition among younger creative workers
D) all of these
E) a and b