Here is the item again:

When the cell phone began to chime in her book bag, (A) Jasmine froze in her seat (B) as all eyes in the room darted from her to Mr. Williams. (C) A professor who tolerated no interruptions during a lecture.

You correctly realized that the period after Mr. Williams created a fragment. A professor who tolerated no interruptions during a lecture is an appositive. When you attach an appositive to the end of a main clause, you need to use a comma.

To fix the problem, you chose to do this:

When the cell phone began to chime in her book bag, Jasmine froze in her seat as all eyes in the room darted from her to Mr. Williams, a professor who tolerated no interruptions during a lecture.

You have correctly employed Punctuation Rule 9:

Main Clause + , + Appositive.

Great move!

Go to the next sentence.

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