A. no, because some of the y-values are paired with two x-values.

b. yes because each x-value has exactly one corresponding y-value.

c. yes, because it touches the y-axis exactly one time.

d. no, because there are no closed circles to show where the graph ends

There's a trick you can do to figure out if it's a function or not:
      You just draw a line straight up and down; if the line passes the graph twice, it is not a function. 

I'm not too sure what the answer is because I haven't done functions since I was a sophomore, but I think it is C.

Sorry if that's wrong, lol.