Which of the following statements about flux are true?

the unit of flux is nm2/c
the total flux through a surface completely enclosing a charge q is q/ε
the total flux through a closed surface can be positive or negative, depending on whether the enclosed charge is positive or negative.
the total flux through any closed surface that does not contain a charge is zero.
when turning a surface inside of an electric field, the maximum flux is achieved if the electric field vector and the surface vector are perpendicular.