Answer:
The layer A is the thermosphere and the layer B is the exosphere.
Step-by-step explanation:
One of the five layers of the atmosphere of the Earth is called thermosphere. It is the fourth layer of the Earth's atmosphere and is situated below the exosphere and above the mesosphere. The thermosphere is the biggest layer of the Earth's atmosphere, and the charged particles found in the thermosphere makes it easier for long distance communication through radio.
The exosphere is the topmost layer of the Earth's atmosphere, here the atmosphere merges with the interplanetary space and thins out. It is situated directly above the thermosphere. It is the layer, which distinguishes Earth's atmosphere from outer space.