Answer:
C. 1/(x^2 +1) > 0
Explanation:
The cube of a negative number is negative, eliminating choices B and D for certain negative values of x.
1/x^2 is undefined for x=0, so cannot be compared to zero.
The value 1/(x^2+1) is positive everywhere, so that is the expression you're looking for.
1/(x^2 +1) > 0