Could someone PLEASE help me with these physics questions? please show work, I WILL RATE GOOD

(3) In the figure below a cylindrical coordinate system has been superimposed on the line charge. The surface is oriented so that it bisects the line charge with the surface area vector parallel to the line charge, Explain why the electric field can not depend on the angle variable t or the variable z, but can depend on r. (4) Based upon these considerations if we want to use Gauss' law to determine the electric field due to this infinite line charge what kind of closed surface should we choose, and why