I believe that the answer would be the impact theory as it is a theory that states that because the moon is of similar composition to the Earth, that it was created by some sort of impact, hence the name of the theory.
Counter current flow is the opposite movement of water against the flow of blood in the fish's gills.
Maybe say something along the lines of " parasites are complex and very harmful" and build off of that statement
The answer is; When the planet is at A it is moving faster than at B.
This is because when the planet is closer to the sun at point A, it is experiencing a stronger gravitation, by the sun, pull than at point B. Therefore, its acceleration due to gravity at point A is higher than at point B.