to enhance the effectiveness of friction to increase the efficiency of the machine to provide an additional source of energy to produce more thermal energy on the machine
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Machines are often full of moving parts that rub against each other. In machines, a lubricant such as oil is often applied to these moving parts. Why is this oil necessary?
Possibilities:
- to enhance the effectiveness of friction
- to increase the efficiency of the machine
- to provide an additional source of energy
- to produce more thermal energy on the machine

to increase the efficiency of the machine