The subject is what the verb agrees with in number. An irate landlord is at the door. Two irate landlords are at the door. The whole subject is the grammatical subject plus all the words that modify it. Matilda ate all the cheese.
Patriotism is the last refuge of the scoundrel.
An irate landlord is at the door. The ability of the city to manage education is an accepted fact. The simple subject is the smallest word inside the whole subject that determines whether a verb will be singular or plural. The books that each person must read are listed. The ability of the city to manage education is an accepted fact.