A laboratory study compared learning from text in two conditions, one with underlining of important terms and one without underlining, found that the underlining group did better on factual items. Marina then conducted a studywith tenth-grade history students and compared one group that read a chapter with the important text underlined and one group that read a chapter without any underlining. Marina's study illustrates an example:________

a. test for reliability.
b. internal validity study.
c. replication study.
d. regression study.