Answer:
I am a mountain at night, meadow at day. What am I?
I transfer oxygen from the atmosphere to your blood
Whoever made me doesn't want me. Whoever bought me doesn't need me. Whoever uses me doesn't know me. What am I?
I make billions of dollars selling windows. Who am I?
The dirtier I get, the whiter I am. What am I?
What language does a billboard speak?