The correct answer is: D. No error
The sentence is grammatically correct. The word “than” is used to compare two things. In this case, the two things being compared are margarine and butter. The sentence is saying that many health-conscious people prefer margarine to butter.
The word “prefer” is a verb that means to like one thing better than another. In this case, the people are saying that they like margarine better than butter.
The word “margarine” is a noun that means a spread made from vegetable oils. It is often used as a substitute for butter.
The word “butter” is a noun that means a spread made from milk fat. It is often used on bread or toast.
The sentence is clear and easy to understand. It does not contain any errors in grammar or punctuation.