You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each 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?
(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
B