Much of Tibet lies at altitudes over 18,000 feet where the ...

[robinn137]

Much of Tibet lies at altitudes over 18,000 feet where the pressure is about 500 mb. At such
  altitudes, the Tibetans are above roughly:a.
   10 of the air molecules in the atmosphere.
  b. 25 of the air molecules in the atmosphere.
  c. 50 of the air molecules in the atmosphere.
  d. 75 of the air molecules in the atmosphere.

Question 2

Since the turn of this century, CO2 in the atmosphere has:a.
   been increasing in concentration.
  b. been decreasing in concentration.
  c. remained at about the same concentration from year to year.
  d. disappeared entirely.

[olderstudent]

Answer to Question 1

c

Answer to Question 2

a