设向量组 $A: \alpha_1=\left(\begin{array}{c}1 \\ -2 \\ -3 \\ 4\end{array}\right), \alpha_2=\left(\begin{array}{c}2 \\ -4 \\ -6 \\ 8\end{array}\right), \alpha_3=\left(\begin{array}{c}0 \\ 1 \\ -2 \\ 3\end{array}\right), \alpha_4=\left(\begin{array}{c}-1 \\ 4 \\ -1 \\ 2\end{array}\right), \alpha_5=\left(\begin{array}{c}3 \\ -9 \\ -3 \\ 3\end{array}\right)$ ．
（1）求向量组 A 的秩；（2）求 A 的一个最大无关组；（3）把其余向量用最大无关组表出．