Which ecological inquiry method is in ecologist using when he or she sets up a greenhouse and measures the effects of different levels of carbon dioxide on an endangered plant species?

Experimenting

Explanation:

If an ecologist sets up a greenhouse and measures the effects of different levels of carbon dioxide on endangered plant species, he is conducting an experiment. An experiment is a procedure that is meant to provide support, refute or validate a particular hypothesis. It is also meant to be repeatable and logical. Experimenting is an important step in the scientific method.

the crusaders are identified in the painting;

c. by the red crosses on their backs