Which of the following statements about Gauss's law are correct? 1. Gauss's law is valid only for symmetric charge distributions, such as spheres and cylinders. 2. The electric flux passing through a Gaussian surface depends only on the amount of charge inside that surface, not on its size or shape. 3. Only charge enclosed within a Gaussian surface can produce an electric field at points on that surface. 4. If there is no charge inside of a Gaussian surface, the electric field must be zero at points of that surface.