generating wingtip vorticies of the greatest strength
This is a function of the wing. Disregard the gear position.
The strength of wingtip vortices is a function of angle of attack - large AoA leads to stronger vortices. Which conditions give greatest AoA?
Heavy and slow or heavy and fast? Flaps up or flaps down?
Answer A is correct.
Once you get that job this will be backed up by real world experience when you're asked to maintain 230 knots and you're following a 757 that's clean.