Which of the following is considered part of the exosphere?

Well I cant see the choices but here are some facts of the exosphere 
As the highest layer of the atmosphere, the Earth's exosphere contains very thin air and features both lower and upper boundaries. The exosphere's boundaries vary by altitude depending on the level of the sun's activity and solar radiation emissions. There is some debate among scientists as to whether the exosphere should be considered a layer of the atmosphere or a part of space.

The exosphere is the outermost region of a planet's atmosphere. Keeping that in mind, think what's out in space!