The 'burden of proof' is on the plaintiff, since the defendant is presumed innocent until proven guilty. [=the plaintiff must prove that the defendant is guilty]
The 'tax burden' has been falling increasingly on the middle class. [=middle class people have been paying a greater portion of taxes]
For the rest of his life he 'was burdened' with the knowledge that he had done nothing to help them.
(..) (GASPING) (MOANING) (SPEAKING ELVEN LANGUAGE) You're late. Merriment can sometimes be a heavier burden than battle. Then you're doing one of them incorrectly. (CHUCKLING) Perhaps. How fare the stars? HEIMDALL: Still shining. (..)2013 Thor: The Dark World