According to the OECD and the UNModel Tax Treaties, nonresident companies may be taxed by a tax treaty state if they maintain a permanent establishment within that state.  Which of the following are examples of permanent establishments?
A、Branch offices.
B、Building sites, construction projects, and assembly projects that last for more than twelve months.
C、Mines, oil and gas wells, quarries, and other places for extracting natural resources.
D、All of the above.