Which of the Following Are Rational Functions:
A) $y=\frac{x^{2}-3}{x^{4}}-\frac{1}{4 x^{2}}$ B) $y=\frac{3^{x}-4}{3^{x}}$

Multiple Choice

Which of the following are rational functions:

A) $y=\frac{x^{2}-3}{x^{4}}-\frac{1}{4 x^{2}}$
B) $y=\frac{3^{x}-4}{3^{x}}$
C) $y=\frac{3 \sqrt{x}+4}{x^{3}-4}$
D) $y=\frac{3 x^{-4}}{3+x^{4}}+\frac{x^{-3}}{1-x^{-3}}$