Take another look at the item:

My appliances are always hungry. (A) For example, the dryer will eat underwear, (B) and the microwave will suck off half a frozen dinner (C) while it is cooking.

You wanted to do this:

My appliances are always hungry. For example, the dryer will eat underwear, and the microwave will suck off half a frozen dinner, while it is cooking.

Adding a comma after dinner is an error. While it is cooking is a subordinate clause. When you connect a subordinate clause to the main clause in front, you rarely use punctuation.

You might want to review the rules.

Go back to the sentence to try again.

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