The correct answer is: D. No error
The sentence “One of the members expressed doubt if the Minister was an atheist” is grammatically correct. The word “if” is used to introduce a clause that expresses a condition or possibility. In this case, the clause “if the Minister was an atheist” expresses the possibility that the Minister does not believe in God. The word “doubt” is used to express uncertainty or lack of belief. In this case, the member is expressing uncertainty about whether the Minister is an atheist. The sentence is clear and easy to understand, and there are no grammatical errors.
The other options are incorrect because they contain grammatical errors. Option A, “One of the members expressed doubt,” is incorrect because it does not include the word “if.” Option B, “expressed doubt,” is incorrect because it does not include the subject of the sentence, which is “One of the members.” Option C, “the Minister was an atheist,” is incorrect because it does not include the word “if.”