Final answer:
The comma in the sentence should be replaced with a period to create two separate sentences.
Step-by-step explanation:
The comma in the sentence 'When confronted about his extended absence from work, Ernest offered a flimsy excuse.' is not the best choice. Instead, we should replace it with a period to create two separate sentences: 'When confronted about his extended absence from work, Ernest offered a flimsy excuse. He was unable to find his car keys.' This makes the meaning clearer and improves the flow of the sentences.
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