Take another look at the item:

Mackenzie had to leave the room, (A) for her father was noisily crunching raw radishes, (B) which produced so annoying a sound (C) that studying was impossible.

You wanted to do this:

McKenzie had to leave the room, for her father was noisily crunching raw radishes, which produced so annoying a sound; that studying was impossible.

Adding a semicolon after sound makes a fragment. That studying was impossible is a subordinate clause. You cannot connect a subordinate clause with such a strong mark of punctuation.

You might want to review the rules.

Go back to the sentence to try again.

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