I live in PA and studied from
www.cristcdl.com and the questions from that site were word for word how they are on the actual test you take at you dmv.
Click on "online testing center"
then study ALL pages/questions from "General Knowledge", "Air brakes", and "combination vehicle" sections.
You will end up with a few headaches, but when you go to the dmv and your screen says "congratulations, you passed", it will all be worth it.