A researcher carries out a study examining the effects of a new science program on scores on a standardized science test. He chooses two seventh-grade classes to carry out the study. After the study is done, he finds that the group that received the new program performed better than the control group. He also discovers, however, that the group he chose to receive the new program had better prior science achievement. In this study, the prior science achievement is ______. Group of answer choices an extraneous variable the independent variable the dependent variable a moderator variable