![](https://www.ebk.net.cn/tikuimages/2/2018/600/shoutiniao93/25e4fa755e8fe83cbd88ecd3f2e73bf8.png)
如图:在平行六面体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)中,\(M\)为\(A_{1}C_{1}\),\(B_{1}D_{1}\)的交点\(.\)若\( \overrightarrow{AB}= \overrightarrow{a}\),\( \overrightarrow{AD}= \overrightarrow{b}\),\( \overrightarrow{AA_{1}}= \overrightarrow{c}\),则向量\( \overrightarrow{BM}=(\) \()\)