Astudent is investigating the effect of plants on inbox air quality and states if plants are added to an indoor environment the air quality will improve this statement is an example of. a. a theory. b. a procedure. c. observations
d. a hypothesis

So all we know is that the student stated something ("if plants are added to an indoor environment the air quality will improve "). This is only a statement - it's not a test whether this statement is true yet.
 
So the correct answer is: it is a hypothesis.

This is the most closely resembles the model.