Gaya APA

Chall, J, S., Conard, S, S. (1991). Should textbooks challenge students?: The case for easier or harder books . New York: Teachers College, Columbia University.

Gaya MLA

Chall, Jeanne, S., Conard, Sue, S. "Should textbooks challenge students?: The case for easier or harder books". New York: Teachers College, Columbia University, 1991. Text.