Answer:
The celestial sphere is a fictional sphere to which all celestial objects can be projected.
Explanation:
At any time an observer can see only the half of celestial sphere because the other half lies under the horizon. The celestial sphere is the medium used for sphere astronomy. The celestial sphere does not have a defined magnitude. It can be infinite or at least really big.
I think the correct answer from the choices listed above is option A. The Rift Valley in Africa is an example of the African plate is breaking apart to form two separate plates.A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault.