Use the map below to answer the following question: Map of Europe and North Africa labeled, Spread of Christianity. Dark green indicates Christian areas, 325 AD. The dark green areas are small, isolated patches surrounding the Mediterranean Sea. Light green indicates Christian areas added by 476 AD. Most of Spain, Gaul, Italy, Greece, and Asia Minor are light green. The light green extends to the European inland, and as far north as parts of Great Britain. It also extends to part of Egypt, Syria, and the North African Mediterranean coast. A grey line indicates the boundaries of the Roman Empire, 476 AD. This line extends around the Mediterranean, from North Africa in the south, beyond Jerusalem to the east, and into northern Gaul.
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Where did Christianity mainly become established in the first 300 years of its existence?

the coastal areas, near cities
the countryside, away from the coast
the islands of the Mediterranean Sea
the mountains between Italy and Gaul