The correct statements are:
- Carbon dioxide in the atmosphere is important for plants;
The carbon dioxide is one of the most important gases for the plants. The reason for that is that the plants use the carbon dioxide for the process of photosynthesis, which is the process through which they make their own food.
- The troposphere gets colder the higher you go;
The troposphere is the warmest at its lowest parts, and the coldest at its highest parts. The reason for that is that the land and the water manage to absorb a lot of heat, the heat radiates from them, which in turn makes the lower parts of the troposphere warmer as they are more exposed to it.
- The ozone in the stratosphere protects us from ultraviolet radiation;
The ozone layer is crucial for the survival of the living organisms on the Earth. It is the layer that manages to absorb mot of the ultra violet radiation from the sun. If this layer doesn't exist, the living organisms will be fried to death.
- The amount of water vapor in the air is nearly constant;
The amount of water vapor in the atmosphere (as a whole) is nearly constant, though there are differences from region to region. The main reason for this is that there is constant evaporation, but also there's always precipitation, thus it balances itself.
