Every Sentence must has a subject and verb.subject &
verb in sentence must agree in Person and Number.
That means, when subject is singular in sentence, verb is also is singular Or Subject is plural in sentence .verb is plural.
Example: 1.The boy plays football. (singular verb)
2.The boys play football. (Plural verb)
[singular verb require s/es]
Rule: 1) singular subject accept singular verb
Example: 1.The Headmaster wants to speak to you.
2. He is a good boy
Rule1.A)Books name ,Subject name,country names seems plural but its to be singular.so verb will here singular
Example: 1) Cultural studies gives a new meaning of culture(Subject name)
2) The United States has a big Navy. (country name)
Rule:2.Plural subject accept plural Verb.
Example:1)The boys play football.