The author says habits are harmless unless injurious and that most of us are mainly made up of them. They simplify the machinery of living by letting us handle a multitude of things automatically; if each needed fresh thought, life would become hopelessly confused. So habits make living easier. The author presents the automatic quality as a benefit, so options with a negative colour, such as making life difficult or mechanical, miss the tone.
Why each option is right or wrong
(a) Opposite of the passage: habits are said to simplify life and prevent confusion.
(b) Precision is never mentioned; the benefit stated is simplicity and ease.
(c) Correct: habits let us do many things automatically, saving us from an impossible confusion of fresh decisions.
(d) The passage praises the automatic ease habits bring; it does not complain that they make life mechanical.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.