Wire (1) – A wire would have the graph of a fixed gradient – there is very little change in resistance of a wire.
Filament lamp (2) – The resistance of the metal within the lamps increases with temperature. The curve of the gradient on a Filament lamp (current x voltage graph) would show that the lamp is reaching it’s working current.
Diodes (3) – The voltage increases as resistance decreases. Semiconductor diodes only allows current to flow in one way (forward)
(Reminder that potential difference is voltage)