"This one, such a large ship! What does it transport?"
In one long slow motion I propelled myself to the other end of the laboratory and glanced over at the screen of the computerized English lesson. "Oh, that is an oil tanker. It transports petroleum; the raw material which is refined into hydrocarbon-based fuels."
There was a pause as he looked up some of the terms I had used.
"You burn hydrocarbons? For what purpose?"
"To power internal combustion engines, which drive many of our personal transportation devices and other machinery."
"How impractical!" he squawked.
"Well, we're trying to stop," I said, apologetically.
"Why would you even begin to burn them? Your sun's energy penetrates your atmosphere; your large moon creates substantial tidal forces."
"It was only relatively recently that we learned to capture the potential energy of photons. And we still have not achieved full efficiency."
Another pause as the guest considered. "For my species, devices to capture energy from the sun were one of the first elementary discoveries. The... solar panel as you would call it... is one of our rudimentary devices. It's mastery is synonymous with the separation of our people from wild animals."
"In my people, the corresponding discovery was that of fire."
The visitor blinked an eye slowly. "How very interesting," he declared, "that explains so much."