Final answer:
A very steep slope on the voltage-current graph of a diode indicates the dynamic resistance is very low and approximately constant over a range of voltages.
Step-by-step explanation:
If a diode on a graph exhibits a straight line with a very steep slope after being switched on, this suggests that the dynamic resistance of the diode is very low. Considering that the resistance remains constant over a range of voltages while the current increases, the dynamic resistance can also be understood to be approximately constant in that voltage range. A steep slope in a voltage-current graph for a diode implies that small changes in voltage will cause large changes in current, indicating a low resistance because a steep slope corresponds to a high conductance (inverse of resistance). The dynamic resistance is not zero because there is a finite slope, and it is not temperature-dependent solely based on the graph; temperature dependence cannot be determined without further information.