A Study at the U

A study at the U.S.Air Force Academcy Preparatory School demonstrated that students' performances can be affected by teachers' expectations.These results are best explained by the fact that

A) studies in the field are more unpredictable than those in the laboratory.
B) naturalistic observation pointed out differences not controlled by a laboratory experiment.
C) the teachers subtly communicated their expectations to the students,which created a self-fulfilling prophecy.
D) the two groups were really not equal in their ability at the start of the experiment.