Final answer:
The sentence with an abbreviation error is sentence 3, where 'Sent.' should be corrected to 'Sen.' for 'Senator.'
Step-by-step explanation:
The sentence that contains an abbreviation error is sentence 3. The error lies in the abbreviation of 'Sent.' which is an incorrect abbreviation for 'Senator.' The correct abbreviation for Senator is 'Sen.' Therefore, the correct answer to the question is option c) 3. It's important to use standardized abbreviations to avoid confusion and maintain professionalism in writing.