Which of the Following Has Not Been Identified by Research

Which of the following has not been identified by research that tries to address the self-selection issue regarding the returns to schooling?

A) When both a high school graduate and a college graduate are placed in the type of job that high school graduates typically fill, the high school graduate would be more productive.
B) When both a high school graduate and a college graduate are placed in the type of job that college graduates typically fill, the college graduate would be more productive.
C) There are many kinds of ability that are rewarded in the workplace.
D) In general, workers appear to choose schooling amounts that maximize lifetime income.
E) All of the above have been identified by the research on the returns to schooling.