What is the most likely reason for the dramatic decrease in the number of children in the average american family?

It seems that you have missed the given options for this question which are the following: a) the increase in religious-based sex-abstinence programs
 b) the availability and use of effective contraceptives
 c) the decrease in the number of people getting married
 d) an increase in same-sex couplings
Based on this, the reason that is most likely why the dramatic decrease in the number of children in the average American family is the the availability and use of effective contraceptives.

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.