12．设$\overrightarrow{a}$，$\overrightarrow{b}$是两个不共线的非零向量，则"$\overrightarrow{a}+\lambda \overrightarrow{b}$与$\lambda \overrightarrow{a}+4\overrightarrow{b}$共线"是"$\lambda =2$"的$($　　$)$