Take a look at the item again:
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 period after radishes makes a fragment. Which produced so annoying a sound ... begins a subordinate clause. Remember that a subordinate clause cannot stand alone as a complete sentence.
You might want to review the rules.
Go back to the sentence to try again.