Cho ba vectơ 

Câu hỏi: Cho ba vectơ $\stackrel{\rightharpoonup }{a}=\left(3;-1;-2\right)$, $\stackrel{\rightharpoonup }{b}=\left(1;2;m\right)$, $\stackrel{\rightharpoonup }{c}=\left(5;1;7\right)$. Xác định m để $\stackrel{\rightharpoonup }{c}=\left[\stackrel{\rightharpoonup }{a},\stackrel{\rightharpoonup }{b}\right]$

A. m = - 1

B.m = - 9

C.m = 1

D.m = 9