Determine if the statements below are true or false. (a) the area vector a of a flat, oriented surface is parallel to the surface. true false (b) if s1 is a rectangle with area 1 and s2 is a rectangle with area 2, then 2 f · da s1 = f · da s2 . true false (c) if s is the unit sphere oriented outward and f · da s = 0 then f (x, y,z) is perpendicular to x i + y j + z k at every point of s. true false