Final answer:
The Romans invaded the Celts and their religion in 55 BCE. They conquered the Celts, assimilating them into the Republic and spreading Roman culture. The Romans also invaded Britain and imposed their culture there in 43 CE.
Step-by-step explanation:
The Romans invaded the Celts and their religion in the year 55 BCE (option B).
After an earlier raid in 387 BCE, the Romans began to expand beyond Italy and conquered the Celts, assimilating them into the Republic. Roman culture and influence spread among the Celts, who adopted Roman customs and served in the Roman armies.
It is also worth noting that the Romans had a significant impact on Britain. In 43 CE, the emperor Claudius invaded Britain and incorporated the southern region into the Roman Empire, imposing Roman culture and constructing forts and roads.