Mystery #4Tier 2-3body / lungs
Why is it harder to breathe high up a mountain?
Climbers high on a tall mountain gasp for breath and sometimes carry oxygen tanks, yet the air around them still looks perfectly normal. There's air to breathe, so why isn't it enough?
Your guess
What's your hunch about why it's hard to breathe high up, even though there's still air?
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
Make a guess to unlock the hints and the answer.