Question

The mountain pine beetle which is considered a threat to pine trees is expanding into a new habitat. Which revision corrects the punctuation of the sentence? 1. The mountain pine beetle, which is considered a threat to pine trees is expanding into a new habitat. 2. The mountain pine beetle which is considered a threat to pine trees, is expanding into a new habitat The mountain pine beetle, which is considered a threat to pine trees, is expanding into a new habitat. 3. The mountain pine beetle which is considered a threat, to pine trees, is expanding into a new habitat

Answer 1

Answer: The mountain pine beetle, which is considered a threat to pine trees, is expanding into a new habitat

Explanation: The commas go around the additional information in the sentence in a way which ensures the sentence could still be read without them. If you took the section away, you would have "The mountain pine beetle is expanding into a new habitat."

So, commas go around non-essential clauses that add information.