The definition of a function is a relation where every input (x value) is paired with exactly one output (y-value).
A. Not a function, because you have (300, 9) and (300,7). The x-value 300 is paired with two different y-values, 9 and 7.
B. Not a function. (260, 4) and (260, 2)
C. Is a function
D. Not a function. (225, 4) and (225, 2)
