Answer: Choice B
Reason:
Choices A, C and D have repeated x values. It allows us to rule them out.
Table A has x = 6 repeating. Table C has x = 3 and x = -3 repeated. Table D has x = 4 and x = 5 show up twice each.
Whenever we have repeated x values, it indicates we do not have a function. A function is only possible when each x value goes to exactly one y value only.
Table A has the input x = 6 lead to y = 2 and y = -2 at the same time. Table C and table D are a similar story. So this is another way to rule out choices A, C and D.
Luckily table B has no repeated x values. Each x input leads to exactly one and only one y output. Therefore, table B is a function.
Side Note: the y values can repeat, but the function won't be one-to-one.
