5. It is known that after 100 years, cadmium retains $95.76 \%$ of its original mass. Let the remaining mass of a mass of 1 after $x$ years be $y$, then the functional relationship between $x$ and $y$ is ( ).
(A) $y=(0.9576)^{\frac{x}{100}}$
(B) $y=(0.9576)^{100 x}$
(C) $y=\left(\frac{0.9576}{100}\right)^{x}$
(D) $y=1-(0.0424)^{\frac{x}{100}}$
5. A