Which of the following is not considered a nordic country? a. iceland b. ireland c. norway d. sweden

The Nordic countries are a geographical and cultural region comprising five northern European states and three autonomous regions:  

The Scandinavian countries (Sweden, Denmark and Norway) plus Finland and Iceland that were included because of their geographical proximity and cultural origin. In addition, the autonomous regions of Faroe Islands and Greenland (belonging to Denmark) and Åland (belonging to Finland) are also included.

These countries have so much in common in terms of lifestyle, history, language, religious level and social structure; and their flags share  in common the Scandinavian cross.

As we can see, Ireland does not appear on this list. Therefore it is not considered a Nordic country.

they use tree rings to figure out weather patters.