______ is the most important gas for the survival of living organisms.

(a)

Helium

(b)

carbon-di-oxide

(c)

oxygen

(d)

oxygen

The lowest layer of the atmosphere is__________.

(a)

Troposphere

(b)

Stratosphere

(c)

Exosphere

(d)

Mesosphere

_______  reflects radio waves

(a)

Exosphere

(b)

Ionosphere

(c)

Mesosphere

(d)

Stratosphere

The average global surface temperature is ______ 

(a)

120°C

(b)

130°C

(c)

140°C

(d)

150°C

Temperature ______ from the equator to pole

(a)

Increases

(b)

no change

(c)

decreases

(d)

stable