Read this sentence from Rhadika's biographical essay about Joan of Arc. Which revision best provides a more formal tone?

OI think Joan of Arc was cool because she showed that women can't easily be kept down.

O I believe that Joan of Arc shows that women can't easily be kept down.

O We think Joan of Arc was important because couldn't easily be silenced. Many historians think that Joan of Arc helped prove the important role of women.

O Joan of Arc was definitely important since she proved to be a really cool woman.​