Hello. Your question is incomplete. However, when researching, I managed to find a question like yours and found that you forgot to mention that the question wants you to determine which is the best reference point in this scenario.
Answer:
The best point of reference is the starting position of the toy car.
Explanation:
To study the movement of the car it is necessary for Sudhi to establish a reference point, so that she can calculate all the variables associated with this movement. The best variable in this scenario is the starting position of the car, when it is still on the ramp. Thus, Sudhi needs to determine the distance between the car and the ground, that is, what the car's starting position is. She will be able to discover this when determining the height of the ramp.
 
        
             
        
        
        
Sulfur<span> is an important structural atom in most </span>proteins<span> as </span>sulfur amino acids. It defines its structure. <span>The </span>sulfur<span>-containing </span>amino acids<span>, </span>can<span> be converted into each other but neither </span>can<span>be synthesized in humans. Hope this answers the question. Have a nice day.</span>
        
                    
             
        
        
        
The correct answer is D, white blood cells.
We know that red blood cells deliver nutrients and are not apart of the immune system; platelets are responsible for coagulation, which has nothing to do with the immune system, and plasma is a substance that, again, has nothing to do with immunity. White blood cells are the only things that fight disease (antibodies are white blood cells)! 
I hope I helped!
(By nothing I meant very little to none).
        
                    
             
        
        
        
Answer:
Explanation:
Gas exchange occurs at the alveoli in the lungs and takes place by diffusion. The alveoli are surrounded by capillaries so oxygen and carbon dioxide diffuse between the air in the alveoli and the blood in the capillaries.