What is the U.S. policy in Central America? 

Once again, this is too broad of an area of research for a college level paper.  The problem here is that Central America is too big of a geographic and political region.  U.S. has a record of relations with each on the Central America countries that varies throughout history and political environments.  For example, a much more clearly defined research question within the broader scope of discussion on the U.S. political relations with Central America could be:

What is the history of the United States involvement in the country of El Salvador?