7. If the irreducible fraction $\frac{p}{q}\left(p, q \in \mathbf{N}^{*}\right)$ is converted to a decimal as $0.18 \cdots$, then when $q$ is the smallest, $p=(\quad)$
A: 9
B: 7
$\mathrm{C}: 5$
$\mathrm{D}$ :
2
Answer D.
Analysis From the problem, we get
$$
0.18<\frac{p}{a}<0.19 \Leftrightarrow \frac{100 p}{19}<q<\frac{100 p}{18}
$$

It can be seen that as $p$ increases, the lower bound of $q$ keeps increasing.
When $p=1$, there is no integer $q$ that satisfies the condition; when $p=2$, $q=11$ satisfies the condition, so $q_{\min }=11, p=2$.