Final answer:
The correct completion of the sentence is 'Careful as he was, John still made several errors in his report.' This indicates that despite being careful, mistakes were still made. A review of comma rules with example sentences is provided for clarity.
Step-by-step explanation:
The sentence in question should be correctly completed as: Careful as he was, John still made several errors in his report. The word 'as' fits best here as it conveys the meaning of 'despite the fact that'. The completed sentence indicates that even though John was careful, he still made mistakes.
To improve your understanding of comma usage, let's review the sentences you provided:
- I finally found my keys, and I got to work just in time.
- Mrs. Contreras threw out her old coffee table and cleaned the carpet.
- Taking the elevator to the roof, we hoped we could see the skyline and the bay.
- Though Susan wasn't feeling well, she went to the store anyway and bought ice cream, pizza, and candy.
- I let my neighbor borrow my phone because she said hers was tapped by the police.
In cases like these, it's key to remember that commas often follow introductory clauses, separate independent clauses when they are joined by conjunctions, and should not be used between a subject and its verb or between a verb and its object.