How to write Facebook in English?

Facebook is written in English like this: Facebook.

example sentence

The 1 training set owned by Google and Facebook is private.

Training sets like Google and Google? Facebook? It's all personal.

Privacy issues put Facebook in trouble.

Privacy issues have landed? Facebook? Washington is in hot water.

3 Facebook is so convenient.

Facebook? It's so convenient.

Students in Iron School may not drop out of high school and start the next Facebook.

Students in the iron class may not drop out of high school and set up the next school? Facebook.

When Catherine used Facebook, some of her high school classmates began to add her as friends.

When Katherine joined, Some high school classmates of Facebook began to add her as friends.

To our amusement, the boy said that his favorite book was Facebook.

To our interest, what did the boy say was his favorite book? Facebook.