If it's in your laundry area and you already know which ones are the water lines, there's a good chance it's the gas line. I'd try following it back to the source to see if it connects to the gas line, if you can.
Also, you should know that there's a difference between natural gas and liquefied propane or LP. They burn differently, and there will be major issues if you hook an appliance configured for LP up to natural gas and vice versa.
You'll know you have LP if you have a tank nearby, and if so you will probably need to modify the dryer for it. The installers should be able to do this for you for an extra fee. Natural gas is usually delivered by pipes in the ground, and most dryers are set up for that from the factory.
For near enough to every single model not to matter the LP conversion kit is sold separately, also. For Whirlpool and their subsidiaries (Maytag) in particular, their LP kit lineup recently changed just to make matters more confusing, and probably not all retailers are up to date on which model requires which kit. So have fun with that.
TL;DR: Your life will be much easier if your house is served by natural gas rather than propane.
One of my duties in life is maintaining a major appliance e-commerce web site with ~14,500 SKU's. So I might know a thing... or two... about appliances.