Yes, that is exactly what you should tell them. 1  If two clauses are connected with a coordinating conjunction, it's a compound sentence. 2  If two clauses are connected with a subordinating conjunction, it's a complex sentence.
Trains were first- 1784, but cars weren't invented until 1890.
The railroad was first developed in Great Britain. A man named George Stephenson successfully applied the steam technology of the day and created the world's first successful locomotive. The first engines used in the United States were purchased from the Stephenson Works in England.