"from earth to moon" implies endpoints at both locations and it is thus a line segment
A line extends forever in both directions, a line segment is just part of a line. It has two endpoints, and a ray starts at one point and continues on forever in one direction.
Cosmologists refer to a "surface of last scattering" when the CMB photons last hit matter; after that, the universe was too big. So when we map the CMB, we are looking back in time to 380,000 years after the Big Bang, just after the universe was opaque to radiation. But the CMB was first found by accident.
The direction of an electric field is determined from the behavior of a positive test charge that is set free in the electric field.This charge moves along a distinct vector showing the direction of the electric field Therefore the answer is b. a positive charge will move in the field.
