Math find domain restrictions

Question

Which functions has the fewest domain restrictions for real number?

A) f(x)= 1/(x-1)

B) f(x)= 1/(x+1)

C) f(x)= 1/(x^2-1)

D) f(x)= 1/(x^2+1)

Answer 1

per the denominator

A) has one restriction x = 1 not allowed

B) has one restriction x = -1 not allowed

C) has 2 restrictions x = 1 and x=-1 are not allowed

D) has no restrictions

so D is your best answer