Answer:
Step-by-step explanation: Function is defined as, a set that assigns x to y values, each y value associated with x has to be uniques, and there can not be two values for a single x value. Using this defination we can determine which one is a function (A to D).
(A): For x = 3 there are two values of y therefore it can not be a function.
(B): Same is true for x = 3.5, which is that there are two y values associated with the x value.
(C) Similarly, the solid dot represents a value, therefore at x = -3 there are two corresponding y values, therefore it is not a function.
(D) Each x value has a unique y value, and there aren't any two values associated with a single y value. therefore it is a Function.
The answer, therefore, is D.