Answer:
This question is asking to identify the variable in the experimental statement. 
The eye chart is the CONTROL VARIABLE
Explanation:
An experiment consists of several variables to look out for in order to achieve any significant result. These variables are independent variables, dependent variables and control variables. Although independent and dependent variables are the major experimental variables, but control variables are also important. 
A control variable is the variable that remains constant or unchanged throughout the experiment. Any change to the control variable will affect the dependent and independent variables. In this question, the eye chart is the CONTROL VARIABLE because it remains constant or unchanged. The same eye chart is used for the experiment. 
N.B: The distance to the eye chart is the independent variable while the number of letters visible on the line is the dependent variable. Hence, changing the eye chart (control variable) will affect the distance and the number of letters visible. 
 
        
             
        
        
        
Number 1: The Circulatory System is a vast network that contains organs and vessels.
number 2: Arteries have a thick wall which helps a powerful pressure from the heart.
number 3: Without the Circulatory System the body wouldn't be unable to maintain a internal environment.
number 4: The Circulatory and Respiratory system both have gas to help a or animal live in there internal environment.
number 5: Blood vessels brings oxygen to the tissues and absorbs carbon dioxide and other waste products to clear the lungs. And with out oxygen the tissues won't absorb carbon dioxide to clear out the lungs.
number 6: D
        
             
        
        
        
Answer:
A food web consists of many food chains. A food chain only follows just one path as animals find food. eg: A hawk eats a snake, which has eaten a frog, which has eaten a grasshopper, which has eaten grass. A food web shows the many different paths plants and animals are connected.
Explanation:
I hope this helps!!!
 
        
             
        
        
        
Answer:
i think 1 is either b or d
Explanation: