This is not the graph of a linear function. The graph of a linear function is a right line. Then it's not option A. This is the graph of a function, because it passes the vertical line test. Any vertical line that you draw only cuts the function in one point. Then it's not option C. It's not a one-to-one function because it doesn't pass the horizontal line test. There are horizontal lines that cut the graph in more than one point. Then it's not option D.
Answer: Option B. This is the graph of a function, but it is not one-to-one
