Earth's outer layer is composed of seven dominant plates. what is the name of this rigid outer layer?

I believe the correct answer is lithosphere. The Earth's outer layer that is composed of seven dominant plates is the lithosphere.  Earth's lithosphere includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is subdivided into tectonic plates.

The sun's parallax would be 180 degrees, greater than which you can't get.  so a. would be your anwser 

Geothermic gradient is the rate of increasing temperature with respect to increasing the depth in the earths interior. away from tech tonic plates boundaries, it is about 25-40 c/km (72-87 degrees f/mi) of depth near the surface in most of the world.