Which of the following revisions correctly punctuates the underlined portion of the sentence? 'The ancient manuscript which was discovered in a forgotten library contained valuable historical insights.'

The correct answer to the question "Which of the following revisions correctly punctuates the underlined portion of the sentence? 'The ancient manuscript which was discovered in a forgotten library contained valuable historical insights.'" is Option A: manuscript, which was discovered in a forgotten library,.

The other options — B) manuscript which was discovered in a forgotten library,, C) manuscript, which was discovered in a forgotten library, D) manuscript which was discovered, in a forgotten library, — are incorrect for this ACT Exam Prep question. As explained above: The phrase 'which was discovered in a forgotten library' is a non-essential clause, providing extra information. Non-essential clauses must be set off by commas on both sides.