Final answer:
The phrase 'mail-a-letter' contains a noun-verb pair, with 'letter' being the noun and 'mail' as the verb. Subject-verb agreement rules are crucial for proper sentence structure, and vary depending on compound subjects, word order, and indefinite pronouns.
Step-by-step explanation:
The term 'letter' can refer to both a character of the alphabet and a written communication sent via the postal system. In the phrase 'mail-a-letter', 'mail' functions as a verb, and 'letter' is the noun that is the object of that verb, indicating the action of sending a letter through the postal service. This is indeed an example of a noun-verb pair because 'mail' is the action carried out on the noun, 'letter'.
Understanding proper subject-verb agreement is crucial in forming correct sentences where the subject and verb must match in number. For example, compound subjects joined by 'and' usually take a plural verb unless they refer to a single idea or unit. On the other hand, when two subjects are connected by 'or' or 'nor', the verb agrees with the nearest subject. Additionally, it's important to ensure that the verb agrees with the subject when there are intervening words or when the subject follows the verb.