Which sentence contains an error that a spell-checker would not detect?

The sentence that contains an error a spell-checker would not detect is the one where "there" is used instead of the correct form "their." This distinction is important because "there" refers to a place, while "their" is the possessive form that indicates something belongs to the students.

While spell-checkers are effective at identifying misspellings, they may not flag words that are spelled correctly but are used incorrectly in context. Such errors, often related to homophones—words that sound the same but have different meanings and spellings—can easily slip through automated checks. This is why the correct sentence includes an error that a spell-checker would overlook. Understanding the proper use of homophones is crucial for clear and effective communication in writing.