Read the excerpt from a bibliography.

Cleator, P. E. Lost Languages. New York: The John Day Company, 1961.

Cottrell, Leonard. Reading the Past: The Story of Deciphering Ancient Languages. New York: Crowell-Collier Books, 1971.

What is the primary reason for the author to include these entries?

A. to credit two of his sources

B. to guide readers in their research

C. to provide two opposing viewpoints

D. to emphasize the research he completed