1. $\vec{a} 、 \vec{b} 、 \vec{c}$ are three non-zero vectors, $m \in \mathbf{R}$, which of the following operations is incorrect $(\quad)$.
A. $(\vec{a}+\vec{b})+\vec{c}=\vec{c}+(\vec{b}+\vec{c})$
B. $(\vec{a}+\vec{b}) \cdot \vec{c}=\vec{a} \cdot \vec{c}+\vec{b} \cdot \vec{c}$
C. $m(\vec{a}+\vec{b})=m \vec{a}+m \vec{b}$
D. $(\vec{a} \cdot \vec{b}) \cdot \vec{c}=\vec{a} \cdot(\vec{b} \cdot \vec{c})$
1. D. $\vec{a} \cdot \vec{b} \in \mathbf{R}$, then $(\vec{a} \cdot \vec{b}) \cdot \vec{c}$ is parallel to $\vec{c}$. Similarly, $\vec{a} \cdot(\vec{b} \cdot \vec{c})$ is parallel to $\vec{a}$, but the relationship between $\vec{a}$ and $\vec{c}$ is uncertain.