单选题 Directions: Choose the best answer to each of the question or unfinished statement after reading the passage.Managers who remember to say "thank you" to people who work for them may find that those employees feel motivated to work harder. Researchers at the Wharton School at the University of Pennsylvania randomly divided university fund-raises into two groups. One group made phone calls to solicit alumni donations in the same way they always had. The second group--signed to work on a different day, received a pep talk from the director of annual giving, who told the fund-raisers she was grateful for their efforts. During the following week, the university employees who heard their message of gratitude made 50% more fund-raising calls than those who did not.Question: According to the study at the Wharton School at the University of Pennsylvania, it can be known that ( )