Answer:
Because each subject in an experiment has to have equal conditions to ensure the most accurate results. And water temperature is known to impact plant growth. An experiment using different water temperatures is a terribly inaccurate experiment. 
 
        
             
        
        
        
Answer: A. mechanisms for which activity is primarily triggered and shaped by the incoming stimulus information.
Explanation:
Bottom-up mechanism is a process in which a body perceives an incoming stimulus and certain physiological changes occurs in the body working in the direction of upwards that is the signals are transferred to the brain so that the brain could interpret the stimulus. This mechanism suggests the fact that our perceptual experience is based upon the sensory stimuli.