Which of the following sets represents a function?
a. {(3, 5), (-1, 7), (3, 9)}
b. {(1, 2), (3, 2), (5, 7)}
c. {(1, 2), (1, 4), (1, 6)}

A data set can be verified to be a function or not through the vertical line test. In this test, if the data set has points lying on the same vertical line, then it is not a function. This means the points should not have the same x. The answer hence to the problem is B.