Which of the following types of credits would best describe credit cards?
a. closed and secured
b. closed and unsecured
c. open and secured
d. open and unsecured

I believe the answer is: open and unsecured 

Open credit refers to a type of credit that provided money to be borrowed at a certain time when we need it. 
And unsecured credit refers to a type of credit that does not protected by asset collateral.
Credit cards have both of these characteristics.

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.