Which of the Following Is an Example of a Multifactor

Which of the following is an example of a multifactor experiment?

A) Performance on a list-learning task is compared for male and female participants.
B) Recall performance is measured for a 10 item list versus a 50 item list.
C) Amount of forgetting for a word list is measured as a function of number of presentations and word length.
D) Percent recall is compared between a group who studies a list for 20 minutes and a group who studies for only 10 minutes.