4. For any positive integers $n$ and $k(k \leqslant n)$, $f(n, k)$ represents the number of positive integers not exceeding $\left[\frac{n}{k}\right]$ and coprime with $n$. Then $f(100,3)=$
A. 11
B. 13
C. 14
D. 19
$100=2^{2} \cdot 5^{2}$, so $f(100,3)=33-\left[\frac{33}{2}\right]-\left[\frac{33}{5}\right]+\left[\frac{33}{10}\right]=14$. Therefore, the answer is $C$.