Question

Which sentence is punctuated correctly?

Answer 1

Answer: C) After they rested a few days, the aliens revived sufficiently to explore.

Explanation: an independent clause is a phrase that has a subject and a predicate and that has complete meaning on its own. A dependent or subordinate clause is a phrase that doesn't have complete meaning on its own. When we have a subordinate clause followed by an independent clause, we must separate them with a comma, so the correct answer is option C, we have the subordinate clause "after they rested a few days" and the independent clause "the aliens revived sufficiently to explore" separated by a comma.

Answer 2

After they rested a few days, the aliens revived sufficiently to explore.
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In order to check comma placement, swith the sentence around and see if it still makes sense. In this case it would be:
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The aliens revives sufficiently to explore after they rested a few days.