What do you define as southern states and why?
It's your opinion!

My definition/explanation:

In America we mostly consider the south eastern states to truly be the “southern states”, but what about Texas? Texas is very southern but Louisiana is much more “southern” in its culture and geography than Texas

But they’re right next to each other right?

And at what point does southern turn to south eastern? And southwestern? Is Texas the only true “southern” state?

I don’t think anyone will every agree on this so let’s keep it simple with a definition

“A southern state experiences warm and wet climate, goes no further west than the Mississippi River, no further north than the Ohio, and stops at the Chesapeake.”

Hope this helps

Answer (d) the greenhouse effect is primarily caused by car and trucks;

The answer is    d.  central highlands