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 Rogers was the first train in Illinois and the first train to be operated by the Northern Cross Rail Road, a future unit of the Wabash Railroad and today part of the sprawling Norfolk Southern Corporation. Unlike later railroads in Illinois, private entrepreneurs did not develop the Northern Cross.