6. How would you describe the temperature gradient in the stratosphere?
A.It is not related with altitude.
C. It increases with increasing altitude.
B.It stays the same with the altitude.
D. It decreases with increasing altitude.
7. How do shooting stars form?
A. They result from the friction of meteors with mesosphere's gas layer.
B. They are particles suspended in mesosphere that eventually fall into the ground.
C. They are the result of chemical reactions among gases taking place in the
mesosphere.
D. They result from the friction of meteors with a layer of thermosphere full of charged
particles.
8.What is the boundary between Earth's atmosphere and outer space?
A.aurora
B. ionosphere
C. karman line
D. ozone layer
2. What holds the atmosphere of Earth in place?
A.the sun
B. the moon
C. its gravity
D. its rotation
10. How did the photosynthetic organisms initiate the changes in atmosphere?
A. They released oxygen as a product.
B.They were first organisms to reproduce and evolve.
C.They broke down methane into its component elements.
D. They were the first organisms to respire and release carbon dioxide.​