Interpretation of correlational relationships difficult

Which of the following is NOT a specific problem that makes the interpretation of correlational relationships difficult? The dependent-variable problem

The directionality problem

The third-variable problem

Selection bias

High school students in Mississippi, where teacher salaries are low, were found to score better on the SAT than did high school students in California, where teacher salaries are high. According to the author of the Correlation and Causation reading, what is the explanation for this finding?

Mississippi uses the money it saves on teachers' salaries to send students to SAT preparatory classes.

The SAT is a biased test that favors East-coast students.

Only the most advantaged and academically talented students in Mississippi even bother to take the SAT, whereas nearly half the students in California take it.

Poorly-paid teachers do a better job of educating students than highly-paid teachers do

Bruner and Revuski's research with high school students pressing telegraph keys showed that

people are much smarter than pigeons.

people can easily develop superstitious behaviors without even being aware of it.

earning a nickel is not an effective reinforcement for most high-school students.

superstitious behaviors are just as easy to extinguish as they are to learn.