Can anyone kindly explain why this sentence is correct?
Complex musical numbers are a defining characteristic of most Italian
In a comment, John Lawler wrote:
A defining characteristic of Italian films is not a subject; it is a noun phrase that is the predicate of the sentence, following the be form that is the required auxiliary for predicate nouns. He is an idiot, She is a genius, They are the ones, all use predicate noun phrases, following be, using whatever articles those noun phrases use. They are not subjects; they are predicates and they don’t have to agree with anything.