设 $\boldsymbol{A}, \boldsymbol{B}$ 都是 $n$ 阶矩阵, $r(\boldsymbol{A}+\boldsymbol{B})=n$, 则
A. $r\left(\begin{array}{l}\boldsymbol{A} \\ \boldsymbol{B}\end{array}\right)=n, r(\boldsymbol{A}: \boldsymbol{B}) < n$.
B. $r\left(\begin{array}{l}\boldsymbol{A} \\ \boldsymbol{B}\end{array}\right) < n, r(\boldsymbol{A}: \boldsymbol{B})=n$.
C. $r\left(\begin{array}{l}\boldsymbol{A} \\ \boldsymbol{B}\end{array}\right) < n, r(\boldsymbol{A}: \boldsymbol{B}) < n$.
D. $r\left(\begin{array}{l}\boldsymbol{A} \\ \boldsymbol{B}\end{array}\right)=n, r(\boldsymbol{A}: \boldsymbol{B})=n$.