Answer:
People are not aware of their causes and impacts.
Explanation:
First, people just seem to think that a little bit of harm won't impact the world at all, but that little bit for everyone adds up and the magnitude is a lot worse than people would imagine. Next, even if they/we do know the scale, they don't know how to help or are not interested enough to try and fix the problem. We all think that we won't be able to help enough to fix the issue.
The site for gas exchange in the lungs is the alveoli.
To be simple and easy, your answer would be:
1. Mars
2. Mercury
3. Venus
