What Is the Reason for the Discrepancy Between the Findings

What is the reason for the discrepancy between the findings of Murray and Holmes and Swann?

A) Swann used a survey to arrive at his results, whereas Murray and Holmes administered practical tests to collect data.
B) Swann worked with couples who had been together for several years, whereas Murray and Holmes surveyed couples who had recently gotten hitched.
C) Swann did not include same-sex couples in his study, whereas Murray and Holmes included homosexual couples in their study.
D) Swann measured specific features of the self, whereas Murray and Holmes measured global, overall appreciation.