A complex sentence contains a simple sentence and a subordinate clause. The subordinate clause must be attached to a simple sentence or it is a sentence fragment. Look at these examples of a subordinate clause written as a sentence. Each one is a fragment.
Because it is still raining.
While Dad was at work.
These subordinate clauses cannot be used as a sentence. When they stand by themselves, they are fragments.
A subordinate clause must be attached to a complete thought.
Look at these sentences. They begin with a subordinate clause, but they finish with a complete thought.
Because it is still raining, we’ll have to cancel the picnic.
While Dad was at work, someone dented his car.
When you begin with a subordinate clause, be sure to add a complete thought to the end of it.
▶It’s your turn. Add a comma and a complete thought onto the end of this subordinate clause to make a complete sentence. If you drop the dishes. Did you figure out how to end the sentence so it makes sense? Good for you!