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 first car invented and built in 1885 and unveiled in 1886 by Karl Benz. The first car, Benz Patent Motorwagen, is the first car ever made in history powered by gasoline with an engine motorized by an internal combustion.