The range of the function $f(x)=\frac{1}{3-\sin 4x}$ is :

$\left[\frac{1}{4},\frac{1}{2}\right]$ $\left[\frac{1}{2},1\right]$ $\left[\frac{1}{4},\frac{3}{4}\right]$ $\left[\frac{1}{2},\frac{3}{4}\right]$

$\left[\frac{1}{4},\frac{1}{2}\right]$

$f(x)=\frac{1}{3-\sin 4x}$ $-1≤\sin 4x≤1$ $-1≤-\sin 4x≤1$ $2≤3-\sin 4x≤4$ $\frac{1}{4}≤\frac{1}{3-\sin 4x}≤\frac{1}{2}$