<p>A significant factor to include in the budget when buying a car are the costs of fuel and maintenance and the insurance payments.</p>
<p>The error is obvious. `are' should be replaced. But is it awkuard to say buying a car without a subject like people?</p>
<p>Somebody correct me if I’m wrong, but I think “buying a car” is a part of the subject, in this case.</p>
<p>What type of question was this? Identifying an error or choosing a correct alternative (I don’t know the formal name for the latter)? Anyways, the subject of the sentence is A significant factor." The “buying a car” part is auxillary; that is, you can take out this clause and the sentence would still make sense. The best way to fix this sentence (without knowing the question type) would be to make “significant factor” plural to address the numerous factors listed at the end of the sentence. Here is the sentence after the correction (I took out the auxillary part to show you the general idea): Significant factors…are the costs of fuel and maintenance and the insurance payments. When doing any correction, eliminate excess words and focus on the main idea. By ignoring the auxiliary stuff, you experience less confusion and thus are more likely to notice the correct correction.</p>
<p>Yes… First , it belongs to identifying a error. As your explanation, the error can be found easily. But what I think is the auxiliary cause ‘buying a car’. If we do not point out the really person who do the matter, maybe the the sentence can be understood as ‘factors buying a car’. So, I think the sentence looks a litter awkuard.</p>