I would go for B.

A line from the center of the circle to a point on the circle will have its length equal to its radius. Therefore, you have 2 equal sides and the triangle formed will be a 60:60:90 triangle with sides 1:1:sqrt2

To get the area of the triangle, you need to get the hieght of the triangle, since we already have the base (sqrt2)

Split the triangle in half, and we get a 30:60:90 triange with sides

(sqrt2)/2:??:1. Solve and you get 1/sqrt2 for the other side.

so area will be 1/2 (sqrt2) (1/sqrt2) = 1/2

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Impossible is nothing