Question 1041087
for the first, x cannot be 0.(c)
2. x^2-9 cannot be 0, so it is 3 and -3.  (a is best choice)
3.x^2+1 cannot be 0.  No real number is excluded from the domain.
4. x^3-x cannot be 0, so x(x^2-1) cannot, and 0, 1, and -1 cannot be (b,c,d)
Set the denominator equal to 0 and solve.  Whatever the roots are cannot be part of the domain, for one will be dividing by 0.