11. A triangle has vertices at $(0,0)$, $(1,1)$, and $(9,1)$. A vertical line divides this triangle into two regions of equal area. The equation of this line is
(A) $x=\frac{5}{2}$
(B) $x=3$
(C) $x=\frac{7}{2}$
(D) $x=4$
B

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