2.(单选题)2)设直线L_(1):(x-1)/(1)=(y-5)/(-2)=(z+8)/(1)，L_(2):}x-y-6=0,2y+z-3=0,的夹角为( ).A. (pi)/(6)B. (pi)/(4)C. (pi)/(3)D. (pi)/(2)

2.(单选题)2)设直线$L_{1}:\frac{x-1}{1}=\frac{y-5}{-2}=\frac{z+8}{1}$，$L_{2}:\begin{cases}x-y-6=0,\\2y+z-3=0,\end{cases}$则直线$L_{1},L_{2}$的夹角为( ).

A. $\frac{\pi}{6}$

B. $\frac{\pi}{4}$

C. $\frac{\pi}{3}$

D. $\frac{\pi}{2}$