The correct answer is B. Mesosphere.
Step-by-step explanation
The mesosphere is the third layer of the Earth's atmosphere, located above the stratosphere and below the thermosphere. Some of its main features are its thickness of 35 km, its temperature, because the mesosphere becomes colder as the distance from the Earth increases, that is, as the altitude increases. In warmer points, its temperature can reach -5 degrees Celsius, but at other altitudes the temperature can drop to -140 degrees Celsius, so it is considered the coldest of all layers.
On the other hand, the mesosphere is a protective layer for the planet, since it destroys most meteors and asteroids before they can reach the Earth's surface. So, the correct answer is B. Mesosphere.