Final answer:
The compound subject of the sentence 'The cat and dog get along very well' is 'the cat and dog,' requiring a plural verb 'get along' according to standard rules of subject-verb agreement in English grammar.
Step-by-step explanation:
The compound subject in the sentence 'The cat and dog get along very well' is "the cat and dog." This compound subject is made up of two nouns, 'the cat' and 'the dog,' which are joined by the conjunction 'and.' According to the rules of subject-verb agreement in English grammar, when two or more subjects are joined by 'and,' they typically require a plural verb. However, if the elements of the compound subject represent a single idea or are thought of as one thing, then a singular verb would be used.
In this case, 'get along' is the plural verb that agrees with the compound subject, indicating that the cat and dog are considered separate entities that collectively perform the action of getting along. It's important to note that when compound subjects are joined by 'or' or 'nor,' the verb should agree with the part of the subject that is closest to the verb. Furthermore, the verb must agree with the subject even when other words come between them or when the verb comes before the subject.