What are key words and key sentences?

From this paragraph which are some key words? Choose three

Types of Weather

There are several ways of describing the weather. You need to describe the amount of sun, the level of precipitation, the strength of the wind and the temperature. There are also possibly one or two other aspects to think about.

The first thing many people describe is the sun. They say if the weather is sunny or not. When there are a lot of clouds the sun’s light is stopped from reaching the surface of the Earth. When this happens it is said to be dull.

From the following paragraph. Choose one key sentences :

Flood is a type of natural hazard, affecting humans and natural habitats, or even killing them. A flood can also cause severe damage to homes, factories, places in public, etc. Initially, the trees in the forest should not be cut down unethically because they can cause many human disasters, which include flooding. A flood occurs; therefore, it is not possible to absorb the rainwater in the plant root, so water flows directly.

From the following paragraph. Choose one key sentences :

Flood is a type of natural hazard, affecting humans and natural habitats, or even killing them. A flood can also cause severe damage to homes, factories, places in public, etc. Initially, the trees in the forest should not be cut down unethically because they can cause many human disasters, which include flooding. A flood occurs; therefore, it is not possible to absorb the rainwater in the plant root, so water flows directly.