Identifying a Function from a Maclaurin Series

The Maclaurin series for a function $f$ is given by $\displaystyle 1 + \frac{x^2}{2!} + \frac{x^4}{4!} + \frac{x^6}{6!} + \cdots + \frac{x^{2n}}{(2n)!} + \cdots$. Which of the following is an expression for $f(x)$?