To study the effectiveness of a certain adult reading program, researchers will select a random sample of adults who are eligible for the program. The selected adults will be given a pretest before beginning the program and a posttest after completing the program. The difference in the number of correct answers on the pretest and the number of correct answers on the posttest will be recorded for each adult in the sample. Which of the following is the most appropriate inference procedure for the researchers to use to analyze the results?

a. A one-sample 2-interval for a population proportion
b. A one-sample t-interval for a sample mean difference
c. A matched-pairs t-interval for a population mean difference
d. A matched-pairst-interval for a sample mean difference
e. A two-sample t-interval for a difference between means.