A Study Was Conducted to Compare Five New Textbooks

Multiple Choice

A study was conducted to compare five new textbooks. Thirty teachers were asked to rate the textbooks they used in the previous semester, and then they were randomly assigned to one of five new textbook groups (n = 6) . At the end of the semester, teachers' ratings of the new textbooks (Y) were collected. What may be an appropriate covariate for this study?

A) Students' achievement at the end of the semester.
B) Students' rating of the new textbook at the end of the semester.
C) Teachers' rating of the old textbook.
D) Teachers' ethnicity.