Consider the following statements:I.Without the atmosphere, temperature would be well below freezing point everywhere on the Earth's surface.II.Heat absorbed and trapped by the atmosphere maintains our planet's average temperature.III.Atmosphere's gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.Which of the statements given above are correct?

1. A

   I and III only

   I and III only. That drops the heat-trapping line, which is keyed.

2. B

   I and II only

   I and II only. That drops the greenhouse-gas line.

3. C

   I, II and III

   I, II and III. Without the atmosphere the surface would freeze; trapped heat sets the average temperature; CO2 and similar gases absorb and trap radiation.

4. D

   II and III only

   II and III only. That drops I.

Summary. Official Set A key is (c) all three. The atmosphere keeps Earth habitable: without it the surface would be far colder (I); absorbed and trapped heat sets the planetary average (II); greenhouse gases such as CO2 are good at absorbing and trapping long-wave radiation (III). All three are correct.