Answer
b, c, and d are not functions.
Work Step by Step
b. is not a function because there are 3 different y-values for the x-value of 5, and a function must have exactly one corresponding y-value for each x-value.
c. is not a function because the graph does not pass the vertical line test.
d. is not a function because that is an equation for a circle and the graph of a circle does not pass the vertical line test.