Explanation: The point of the proverb "If it is not broken, don't fix it" is that tampering with something which is not an urgent problem is unnecessary. All of the alternatives involve the manager's making some change or taking some action. But the first four represent the manager's action as being a response to a particular existing problem. They are not against the spirit of the proverb. But preventive maintenance, over-hauling the machine before it breaks down, seems to be just what the proverb advises against.(E) is the correct answer.