With regard to the "definite article," I've taught my students the following rules:
1. Use 'the' for the range of mountains, e.g. the Alps, the Himalayas, the Rockies, BUT "Everest" without 'the' as it's just one mountain. (Or Mountain Everest)
2. Use 'the' with unique things, e.g. the Nile, the sun, etc.
One of my students said:
"It's ONLY one Everest, Mr. Hussein, right? so it's unique, and you told us to use 'the' before unique things, so why it's "Everest" not "the Everest"?
What's your suggested answer?