Paul was able to spread Christianity throughout the eastern Mediterranean because a) Pax Romana, a time of peace, made travel easier
b) Roman roads connected all parts of the empire
c) his ability to read and write enabled him to keep in touch with people
d) all of the above

D

Explanation:

You could add the various congregations that he was in contact with. I would say all of the above. Pax Romana actually means a time of peace.

I think the roads contributed to where he wanted to go. If not the Mediterean was available to him.

Where he could not travel to he could write. Consider the names of his letters: Corinthians, Romans, Ephesians etc

So it is all of the above.