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.
In the year 1822, an English inventor, George Stephenson invented the first train that had a steam engine. In 1825, for the first time the public train was operated.