The Heliocentric Theory is that Earth and all other planets all revolve around the Sun and the Sun is the center of the universe, instead of the Geocentric Theory which put the Earth at the center of the universe.
Hope that helped! If so mark me as brainliest please, I’m trying to rank up :)
I believe the answer is B.Karl Marx.
Austria-Hungary had invaded and crossed over into, Serbia and Russia was in an alliance with Serbia, so they felt as though they had to help out. Hope this helps.
