Adrug is one which precedes the use of illegal or illicit drugs.
gateway
prescription
tobacco-based
harmless

A gateway drug is one which precedes the use of illegal or illicit drugs. So, gateway drugs are usually the types of drugs people use before moving on to something heavier and far more dangerous. Many consider marijuana to be a gateway drug, because it can make you feel dependent on it and crave something more. The other options don't make much sense here, as prescription drugs are something your doctor gives you, tobacco-based drugs aren't that dangerous, and harmless drugs are, well, harmless.

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.