C is the correct answer because its index is an odd number (=> positive or negative sign will remain as it is) and it does not have a negative sign behind x, meaning that a negative x will result in a negative y or f(x) and thus fulfilling the second condition.
A and D are wrong because a negative x would result in a positive y or f(x) because it has a even number as an index. This does not satisfy the second condition where a negative x should result in a negative y or f(x)
B is wrong because there is a negative sign behind x which makes the positive x result in a negative y or f(x), or the negative x into a positive y or f(x)
All of them satisfy the first condition, though, where a positive x results in a positive
Therefore answer is C
