How was Roman emperor Constantine 1's adoption of Christianity similar to Charle's Martel's victory in the Battle of Tours?

A - Both events made Christianity the official religion of a nation

B-Both events legalized Christianity in areas where it had been illegal

C-Both events were examples of Christianity victory over islamic forces

D-Both events were examples of Christianity's unifying effects in Europe

The answer is D. Both events were examples of Christianity's unifying effects in Europe.

Both emperor Constantine 1 and Charle Martel used the teachings that written on the bible as the foundation of the law in their kingdom.

When they conquered a certain region, they will impose their religion-based law to the people, making a lot of regions in Europe adopt a similar law even though they're controlled by different kingdoms.