The slope of the tangent to a curve `y=f(x)` at `(x,f(x))` is `2x+1.` If the curve passes through the point `(1,2)` then the area of the region bounded by the curve, the x-axis and the line `x=1` is (A) `5/6` (B) `6/5` (C) `1/6` (D) `1`