Answer:
Correct answer is A Roman legions.
Step-by-step explanation:
A is correct answer because Romans spread their culture within the territories they conquered with the use of power. Roman legions were the ones that spread the might of Roman Empire and while spreading Roman power they also spread Roman culture.
B is not correct as the Roman Senate had a role to arrange political affairs in the country.
C is not correct as there weren't that many explorers, and their role was not that influential.
D is not correct as philosophers didn't have opportunity to spread their beliefs and influence across the whole Empire.