5. To test the idea that the average person should be able to hold approximately seven items in short-term memory, a researcher has participants listen while an assistant reads off a list of words.

Some participants listen to a list of three words.

Others hear a list of 5, 7, 10, or 15 words. Later, all participants are asked to recall as many of the words as they can, and the researcher calculates the percentage of words they were able to recall from the list they heard. In this study the independent variable is the .

a. number of words recalled by the participants

b. percentage of words recalled by the participants

c. number of words heard by the participants

d. type of words heard by the participants