A Researcher Thinks That a Person's Mood Has an Effect

A researcher thinks that a person's mood has an effect on how helpful that person is likely to be.To test this,the researcher has some research participants come to the laboratory where they are first given a test and then either heavily praised or strongly criticized for their test performance.Afterwards,participants are asked to help the researcher's assistant move some heavy boxes into another room.The researcher makes careful note of how many and which participants help with moving the boxes.In this example,the independent variable is ________.

A) type of feedback,praise,or criticism given to the participants
B) whether the participants helped the assistant
C) the researcher's notes and observations
D) the participants test performance
E) the number of boxes participants moved