Which one of the following pairs of gases are the major cause of "greenhouse effect"?

The given diagram represents the greenhouse effect.
$I.$ Greenhouse gases absorb infrared radiation from the earth. The absorbed radiations are again emitted towards the earth's surface,heating it up.
$II.$ $CO_{2}, CH_{4}, CFCs$ and $N_{2}O$ are the gases responsible for the greenhouse effect.
$III.$ An increase in the level of greenhouse gases results in considerable heating of the earth,leading to global warming.
Which of the statements given above are correct?

Which of the following groups of gases is responsible for the 'Greenhouse Effect'?

The current average temperature of the Earth is $...i...$. If the greenhouse effect were absent,the temperature of the Earth would have been $...ii...$.

Identify the correct pair of various greenhouse gases and their contribution to global warming.

The two gases making the highest relative contribution to the greenhouse gases are