# The direction ratio's of two lines $AB,AC$ are $1,-1,-1$ and $2,-1,1.$ The direction ratios of the normal to the plane $ABC$ are

$(a)\;2,3,-1 \quad (b)\;2,2,1 \quad (c)\;3,2,-1 \quad (d)\;-1,2,3$

(a) 2,3,-1