Reminder:
You do NOT use a comma before the AAAWWUBBIS if a sentence ENDS with an AAAWWUBBIS clause.
If a sentence STARTS with an AAAWWUBBIS clause, you DO use a comma after the AAAWWUBBIS clause.
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What is the proper way to combine these sentence fragments?
The dog in the park ran away. Because her owner let go of the leash.