Why price levels of notradeables are lower in poorer countries?

labor is cheaper in poor countries and is used intensively in producing non-tradable goods.

non-tradable goods will be cheaper in the poor countries than in the rich.

The productivity of non-tradables is the same across countries but the low productivity of tradebales will force the prices down for the poor countries.

It is caused by the Balassa-Samuelson effect.

All of the above.

None of the above.