Task: Question Answering
Input (English): 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?  
 (A) to enhance the effectiveness of friction (B) to increase the efficiency of the machine (C) to provide an additional source of energy (D) to produce more thermal energy on the machine
Output (English): B