Take a look at the sentence again:

Derek wanted a ferocious pit bull terrier to scare off burglars, but his apartment complex did not allow dogs as a result, Derek had to settle for naming his goldfish Mr. Jaws and installing additional door locks.

Derek wanted a ferocious pit bull terrier to scare off burglars is a main clause. His apartment complex did not allow dogs is also a main clause. A comma and a coordinating conjunction like but can connect two main clauses.

Go back to the sentence to try again.

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