A researcher conducts observational research on the study habits of college students. When students are aware of the researcher's presence, they are more attentive, focused, and structured. When students are not aware of the researcher's presence, they are inattentive, unfocused, and distracted. Which concept best describes this phenomenon?
A.Impression management
B.The Hawthorne effect
C.Self-fulfilling prophecy
D.The Thomas theorem