What is the complete subject of the sentence: "Everyone in our school is wearing uniforms this year."?
Everyone, subject ( single) of the verb ==is
Everyone in our school ==subject of the sentence.
Keep in mind, determine subject-verb agreement by these ways.
True subject will never be after PREPOSITION. ( little except when starting adverbial issue)
The cost of new cars is high.
Subject of the sentence is here===The cost of new cars, you will not determine it.
The single subject is here==COST, clear? Which ( COST) is not after the preposition.
More? Consult with BETTER ENGLISH by late ( He expired few years ago whom I am indebted to basic English in my early life!) Norman Lewis, an ex professor of English, New York university.