Which of these functions are even?
A. $\displaystyle{f(x)=\frac{\cos(2x)}{x}}$
B. $\displaystyle{f(x)=\frac{\sin(x)}{x}}$
C. $f(x)=x\cos(x)$
D. $f(x)=\cos(x)+\sin(x)$
E. $f(x)=2\sin(x)\cos(x)$
F. $f(t)=\sec^2(t)-1$