The effect of a high wing with zero dihedral is as follows:
Zero dihedral effect
Positive dihedral effect
Negative dihedral effect
Its only purpose is to ease aeroplane loading
The term “dihedral effect” means lateral stability, which is the tendency to roll away from sideslip.
If a disturbance causes an aircraft to drop a wing (roll to one side) it will sideslip towards the dropped wing. This will cause the airflow to approach the fuselage from the dropped wing side. When the air meets the fuselage it will split into two parts with some flowing over the top of the fuselage and some flowing under the bottom. The two parcels of air will then flow back together after passing over/under the fuselage.
For a high wing aircraft (with shoulder-mounted wings) the air which flows over the top of the fuselage is moving upwards when it meets the dropped wing, then downwards when it meets the raised wing. This increases the angle of attack of the dropped wing and decreases the angle of attack of the raised wing. So the dropped wing produces more lift and the raised wing produces less lift. This causes the aircraft to roll away from the sideslip and back towards the wings level condition.
So the answer to this question is “Positive dihedral effect”.
When the lift coefficient Cl of a negatively cambered aerofoil section is zero, the pitching moment is:
maximum.
nose down (negative).
nose up (positive).
zero.
When a cambered aerofoil is set at zero degrees angle of attack it will produce some lift. In order to get it to produce zero lift it must be set at a slightly nose down angle. In this condition the upward lift force produced by the upper surface is equal to the downward lift force produced by the lower surface. So the two cancel out to give zero lift. But the pressure distributions of the upper and lower surface are not identical. The Centre of Pressure of the upper surface is further aft than that of the lower surface. So the upward lift of the upper surface is further aft than that of the lower surface. So these two forces produce a nose down pitching moment.
A “negatively cambered aerofoil” is one in which the greatest curvature is on the bottom surface. (Just imagine a standard aerofoil placed upside down).
So to get zero lift we must set it at a slightly nose up angle. In this condition the upward lift force and the downward lift force are again equal, so there is no overall lift. But the upward lift on the upper surface is now ahead of that on the lower surface, so they produce a nose-down pitching moment.
All of this should be clearly illustrated in your course notes.