At XYZ Corporation, Professor Martinelli Assessed Workers' Job Satisfaction at Pretest

At XYZ Corporation, Professor Martinelli assessed workers' job satisfaction at pretest and posttest using a valid measure; she found that posttest scores were significantly higher than pretest scores. However, during interviews conducted after the post-test, Professor Martinelli found that the intervention had changed how participants interpreted the meaning of the questions on the job satisfaction measure. Professor Marinelli's research was hampered by

A) statistical regression.
B) maturation.
C) a history confound.
D) instrumentation change.