In a function, X does not repeat. Your answer is A.
<span>a (1,2) (2,4) (3,5) </span>there are different x values for each point, so this IS A FUNCTION. <span> b. (1,2) (2,3) (1,5) </span>there are two values of x being 1, so this is NOT A FUNCTION.
<span>c. (1,2) (2,4) (2,6) </span>there are two values of x being 2 so this is NOT A FUNCTION. <span> d. (1,2) (3,5) (3,7)</span>there are two values of x being 3, so this is NOT A FUNCTION.