The true statement about “green house effect” is that it is

caused by combination of many gases
caused by CO2
caused only by CO2, CFC, CH4 and NO2 gases
None of these

The correct answer is A. The greenhouse effect is caused by a combination of many gases, including water vapor, carbon dioxide, methane, nitrous oxide, ozone, and some artificial chemicals such as chlorofluorocarbons (CFCs). These gases trap heat in the atmosphere, which warms the planet.

Option B is incorrect because CO2 is only one of the gases that cause the greenhouse effect.

Option C is incorrect because it only lists a few of the gases that cause the greenhouse effect.

Option D is incorrect because it is not a true statement.