in a function, X does not repeat.
Your answer is A.
a (1,2) (2,4) (3,5)
there are different x values for
each point, so this IS A FUNCTION.
b. (1,2) (2,3) (1,5)
there are two values of x being 1,
so this is NOT A FUNCTION.
c. (1,2) (2,4) (2,6)
there are two values of x being 2
so this is NOT A FUNCTION.
d. (1,2) (3,5) (3,7)there are two values of x being 3,
so this is NOT A FUNCTION.
hope this helps and have a great day!