Final answer:
The corrected sentence should read: "Troy McClure keeps running to check his mailbox; he is waiting for a letter from my cousin." Proper punctuation, capitalization, and proofreading practices are essential for clear and polite communication, especially in written letters.
Step-by-step explanation:
The correct punctuation and capitalization for the student's sentence should be: "Troy McClure keeps running to check his mailbox; he is waiting for a letter from my cousin." The semicolon is used here to connect two independent clauses that are closely related. Additionally, ensure to start the character's name with a capital letter as it is a proper noun.
When writing letters, it's important to use proper grammar, correct spelling, and appropriate punctuation to clearly communicate your message. Good writing practices include proofreading for errors, using features like spelling and grammar checkers, and reading your message aloud to ensure clarity. Remember to avoid using all capitals as it can give the impression that you are shouting.