The gas that shows the most variation from place to place and ...

[s.tung]

The gas that shows the most variation from place to place and from time to time in the lower
  atmosphere is:
  a. ozone (O3).
  b. carbon dioxide (CO2).
  c. water vapor (H2O).
  d. methane (CH4).
  e. argon (Ar)

Question 2

In a volume of air near the earth's surface, __________ occupies 78 percent
  and __________ nearly 21 percent.
  a. nitrogen, oxygen
  b. hydrogen, oxygen
  c. oxygen, hydrogen
  d. nitrogen, water vapor
  e. hydrogen, helium

[frankwu0507]

Answer to Question 1

c

Answer to Question 2

a

[s.tung]

Gracias!

[jomama]

Thanks for the timely response, appreciate it