In order to use Green's Theorem, certain conditions must be met. (a) Which of the following conditions must be true? - F must be in the direction of C. - F = Vf = U R is on the right as we move around the curve C. - R is on the left as we move around the curve C. - F is a smooth field on an open region containing C and R. - C is a piecewise smooth simple closed curve that is the boundary of R.