Which education level has the highest return on investment (roi)?
a high school diploma
b bachelor's degree (4 years of college)
c senior in high school
d roi is equal for all of the above.

The correct option is B.
Having a bachelor degree from a college gives the highest returns on investments. People who go to college usually secure high paying jobs compare to their counterparts who have less education.
The type of college one attends also matter, for instance in USA, the college in the first position, which gives the highest return on investment is Massachusetts Institute of Technology  [MIT].

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