Answer:
The ratio of the potential difference across a metallic conductor to the current in the conductor is known as. 
B. Resistance.
Explanation:
According to ohms law   " the current  passing through a conductor is directly proportional to the potential difference between the ends provided the temperature of the wire remains constant".
What is resistance ?
Resistance is a measure of the opposition to current flow in an electrical circuit
what is a resistor ?
a resistor is a n electric conductor which forms resistance to free flow of electric current, the resistance is measured in Ω
 
        
             
        
        
        
Pretty sure its volcanic ash or magma, hope this helps
        
             
        
        
        
Answer:

Explanation:
Ok, the average speed can be calculate with the next equation:
 (1)
   (1)
Basically the car cover the same distance "d" two times, but at different speeds, so:

and the total time would be the time t1 required to go from A to B plus the time t2 required to go back from B to A:

From basic physics we know:

so:


Using the previous information in equation (1)

Factoring:
 (2)
   (2)
Finally, replacing the data in (2)
