is not a graph of a function
Explanation for correct answer:
The concept of graph is that "A set of points in the plane is the graph of a function if and only if no vertical line intersects the graph in more than one point."
Here is not a graph of a function as there is a vertical line which cuts the circle in more than one points these points are and and the vertical line is the .
(This method is called vertical line test)But are graphs of a function by vertical line test.
Hence, is not a graph of a function.
Hence Option(A) is correct.