In the provided sentences, the one punctuated correctly with a parenthetical expression is:
"The teacher will, of course, be reading all of the essays."
Explanation:
1. In this sentence, the parenthetical expression "of course" is correctly set off by commas. This punctuation is essential to indicate that the expression is an aside or an interruption in the sentence.
2. The commas before and after "of course" help to clearly separate this additional information from the rest of the sentence, making it easier for the reader to understand the main idea being conveyed.
3. By punctuating the sentence in this way, the meaning remains clear, and the parenthetical expression is appropriately integrated into the sentence structure without causing confusion or disrupting the flow of the sentence.