A dichotomous key is defined as a biological tool for identifying unknown organisms to a particular taxonomic level. It is constructed with many levels and series of couplets.
So, by observing the given dichotomous key, it is concluded that the correct answer is Option A- Organism X and Z have at least one observable trait in common in this dichotomous key.
There are so many examples for that in different areas, like TPT1 experiment carried out in our lab recently.Here's one link: http://www.alfa-chemistry.com/tpt1-cas-167218-46-4-item-290583.htm
An estuary is partly enclosed coastal body of water with one or more rivers flowing through it, and with a free connection to the open sea. it would be more of a collection. hope this help have a great day.
In New York is where the busiest is in America