(3 points) For each of the following vector fields, find its curl and determine if it is a gradient field. (a) F = (6ry + 4x3) i+ (3x2 + 2?) j + (2yz - 22) k. curl F F ? (b) G = 3yzi+ (3xz + 2?) j + (3xy + 2yz) k curl G = G ? (c) H = 3yzit (22 - 3xz) j+ (3xy + 2yz) k curl H = H