A, if the charge is different, the potential should be gradually reduced. As can be seen from the image, it should be the same positive charge in the same amount, so A is wrong;

B, in the process from N to C along the positive direction of X, the potential decreases, and the direction of field strength between N and C is along the positive direction of X axis, so B is wrong;

The slopes of C and φ-x graphs indicate the electric field strength. It can be concluded from the figure that the electric field intensity between point N and point D first decreases and then increases along the positive direction of X axis, so C is correct;

D, NC electric field line to the right, CD electric field line to the left, move a positive point charge from point N to point D, the electric field force does positive work first and then negative work, and the electric potential energy decreases first and then increases. So, d is wrong;

So choose: C.