A function relates input to output. Functions can be one to one or many to one. The x values represent the input while the y values represent the output. In the case of one to one, it means that the output has only one corresponding input. Many to one means that there are many input values for one output value. An input value cannot have more than 1 output value. If this happens, then it is not a function. Looking at the options given,
Option A is a function since no input value has more than one output value
Option B is not a function since the output values of 7 and 1 has the same input value of - 1
For option C, the values are (- 3, - 2)' (- 1, 1), (- 1, - 5), (1, 4). It is not a function since the output values of 1 and - 5 has the same input value of - 1
Option D is not a function since the output values of 7 and 1 has the same input value of - 1
The correct option is A