The correct answers are:
- allows fuel to burn;
- is the gas that animals breathe;
- forms ozone that absorbs the Sun's harmful rays;
The oxygen is one of the most important gases in the Earth's atmosphere and it has many roles in it.
This gas is the one that allows the things to burn. If there's no oxygen, that the burning of the things on the Earth would not be possible, including the burning of the fuels.
The oxygen is the gas that enables the life of the animals on the planet. Almost all animals on the Earth use the oxygen to breathe and for their bodily functions, and without it, the animals on our planet will not be able to survive.
The ozone layer is basically a layer in the stratosphere made out of ozone, which is a substance made out of three atoms of oxygen. This layer is very important because it has the property to absorb the harmful rays from the Sun, thus enabling the life on Earth to exist and not be fried to death.