What two factors affect the speed of current flow?

The correct choice identifies the two fundamental factors that influence the speed of current flow in a conductor: material and voltage.

Voltage, often referred to as electrical potential difference, essentially pushes the current through the conductor. A higher voltage can increase the flow of electric charge, leading to faster current flow.

The material of the conductor also plays a crucial role in current flow. Different materials have varying levels of conductivity, which affects how easily current can pass through them. For example, copper has high conductivity and allows electrons to flow more rapidly compared to a material like rubber, which has low conductivity.

The other options do not accurately represent the relationship between the factors influencing current flow. While resistance is an important factor, it does not directly correlate with the question about the speed of the current flow; instead, it is more about how much the flow of current is impeded. Current and capacitance pertain to different concepts in electrical theory, focusing more on charge storage rather than the flow speed itself. Lastly, Einstein's theory, while significant in physics, does not apply directly to the basic electrical concepts governing current flow.