3. Given that $a$ and $b$ are both unit vectors, and their included angle is $\theta$. Then the proposition $p:|a-b|>1$ is the ( ) condition for the proposition $q: \theta \in$ $\left[\frac{\pi}{2}, \frac{5 \pi}{6}\right)$.
(A) Sufficient but not necessary
(B) Necessary but not sufficient
(C) Sufficient and necessary
(D) Neither sufficient nor necessary
3. From the geometric meaning of vectors, we know that
$$
\begin{array}{l}
|a-b|>1 \Rightarrow \theta \in\left(\frac{\pi}{3}, \pi\right) . \\
\theta \in\left[\frac{\pi}{2}, \frac{5 \pi}{6}\right) \Rightarrow|a-b|>1 .
\end{array}
$$