When a Stickleback fish feels threatened, it will flare out its pair of pelvic spines and three dorsal spines, making it difficult for predators to swallow them. 
        
                    
             
        
        
        
Options for the question have not been given. They are as follows:
type of soil
type of plants
exposure to sunlight
method for measuring the growth
Answer:
exposure to sunlight
Explanation:
A scientific experiment has an experimental group and a control group. Control group is included to omit any error in results due to the factors other than the variable factor. Experimental group is the one exposed to different levels of the variable factor.
Here, Carlo wants to determine the the effect of day length on plants' growth. The test variable here is thus the duration of sunlight. In experimental group, this duration will be changed to determine its effect. In control group it will be kept constant so that results from other factors can be excluded from the observed experimental result. 
 
        
             
        
        
        
The sustainable use of land means using the spare land in such an activity which supports the society and benefits the environment. 
In such a situation if a land is found spare then a park should be constructed on it. 
This will create an recreational activity spot for the society and they will be able to spend their leisure time with fun. 
Also there will be less pollution and harm to environment will be lowered by greenery and trees in the park.
Learn more at brainly.com/question/24353052
 
        
                    
             
        
        
        
Explanation:
Glycogen is a complex carbohydrate that the body can easily and rapidly convert to energy. Glycogen is stored in the liver and the muscles. Muscles use glycogen for energy during periods of intense exercise. The amount of carbohydrates stored as glycogen can provide almost a day's worth of calories.
 
        
             
        
        
        
Answer:
1 unit
Explanation:
Each tropic level gets 10% of the energy from the last level it consumed.