A researcher pretest a group of participants to determine their attitudes toward the use of alternative energy sources to replace crude oil. The researcher then initiates a program to convince them that they should invest in such alternatives. During this time, the price of gasoline rises $.50 per gallon. At the end of the program, The researcher retestes and finds that the participants are much more positive in their attitudes. What threat to internal validity most likely accounts for this change? A. History
B. Maturation
C. Testing
D. Regression toward the mean