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.
If you take the steam car models into consideration, the first car ever made was the steam car built by Ferdinand Verbiest, but if you only take the gasoline powered models into consideration, the distinction of being the first car goes to the car invented by Karl Benz in 1885.