Well, it depends. Technically all of those answers could SHAPE culture, but language, religion, and government are the best answers. People can still practice their culture despite where they are in the world, after all. So A, B, and C.
Congress can use the mail, free of charge, to mail out political letters and such.
I believe the answer is: precedent
In social setting, we can see a precedent in court ruling.
When a supreme court ruled a controversial case, the other courts would most likely use the ruling as a precedent to settle similar cases that might appear in the future.
What passage? I need to see the passage