Solution:

To determine who must do the most positive work:

- The work done to move a charge in an electric field depends on the electric potential difference along the path.
- The electric field lines point from higher to lower potential.
- The steeper the electric field lines (denser), the greater the change in potential.

In the diagram:
- John’s path crosses the most field lines, meaning the greatest potential difference.
- Thus, John must do the most positive work to move the charge.