we know that
A function is a binary relation over two sets that associates every element of the first set, to exactly one element of the second set
that means
For one value of x , there is only one value of y
In this problem
we have the points
(3,2) and (3,4)
so
For one value of x we have two values of y
therefore
you need to remove (3,2) or (3,4)
The answer is the option C
