The idea that religion and government are separate is

This idea is actually often referred to as a full phrase - "The Separation of Church and State" - but it also has a shorter name, "Secularism" (I assume that this word was among your options). This idea has Greek roots, and became more popular during the time of Enlightenment. 

Currently, as of february 2016, an american traveling in france would be by the exchange rate. the weakness of the euro and the strength of the us dollar means that items in france cost less to an american than they otherwise would. of course, if this trend reverses and the us dollar weakens and the euro strengthens, such as was happening in early 2008, an american traveling in france would have an adverse experience because items would cost relatively more.