Which table does not represent a function? *

X is the value of input, f(x) is the output. if an input produces more than one output, the table does not represent a function.
In this case, table D is not a function. the x value 0 has three different output values, -1, 4, and 6; the input 2 also has three different output values.
While in A, B, C, every x value has only one corresponding y values (Note: these y values can be equal.)