Solution:
To determine if a graph is a one-to-one function, we use the Horizontal line test.
According to the Horizontal line test, If a horizontal line intersects a function's graph more than once, then the function is not one-to-one.
Thus, from the given options, we have
We see that in graph A, the horizontal line intersects the graph more than once.
Hence, graph A is not a one-to-one function.