What are the two primary factors determining voltage rise on a transmission line?

The correct choice highlights the significance of the strength of the bus at the closed end and the length of the line being energized as the two primary factors influencing voltage rise on a transmission line. When a transmission line is energized, the voltage at the closed end (or bus) serves as the reference point. The higher the voltage level at this point, the greater the potential for voltage rise along the line, as the energized line interacts with the characteristics of the load it serves.

Moreover, the length of the line is critical because it impacts the line's inductive and capacitive properties, which can influence voltage levels. A longer transmission line can lead to increased inductance, which might affect how the voltage changes along the line due to varying load conditions. Therefore, understanding these two factors allows operators to predict and manage voltage levels effectively along transmission lines.

In contrast, the other options do not effectively encompass the main drivers of voltage rise in transmission systems. For instance, factors like the resistance of the line or temperature could play a role in overall efficiency and performance but do not directly correlate with voltage rise as the combination of bus strength and line length does.