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. Because her
father was noisily crunching raw radishes, which produced so annoying a
sound that studying was impossible.
Adding a period after room makes a fragment. Because her father was noisily crunching ... 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.