Answer:
The correct option is A.
Explanation:
A relation is called a function if for each values of x, there exist a unique value of y.
A graph show a function if it passes the vertical line test. It means the function intersect each vertical at most once.
From the given graph it is clear that the graph passes the vertical line test because the the function intersect each vertical at most once and for each values of x, there exist a unique value of y.
Hence the correct option is A.