Answer:
I make billions of dollars selling Windows. Who am I?
The more I appear The less you see. So riddle me this: What could I be?
Soldiers fight it but never changes.
You use it between your head and your toes, the more it works the thinner it grows. What is it?
Which is the oldest tree?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.