Which of the following illustrates the concept of equality of opportunity?
a. public schools may not exclude students because of their sex or race.
b. citizens must obey the tax laws but may work to change them.
c. government may limit the beliefs and ideas of individuals.
d. senators consider testimony both for and against supreme court nominees.

The correct answer is A: Public schools may not exclude students because of their sex or race. If public schools would exclude students because of their sex or race, their opportunities wouldn't be equal. Equal opportunity  is a stipulation that all people should be treated similarly, unhampered by artificial barriers or prejudices or preferences, except when particular distinctions can be explicitly justified. The one of the most important points of this concept is that the important jobs in society should go to those "most qualified", and not to persons for arbitrary or irrelevant reasons, such as circumstances of birth, upbringing, having well-connected relatives or friends.