Answer:
75% 
Explanation:
The real answer is 80% and 75% is closest so uhm yea 
 
        
             
        
        
        
Answer:
the answer is actually c 
Explanation:
Cold air is more denser than hot air because ,when cold air of some density, say 'd' is heated, the molecules/atoms move apart from each other and so the volume expands. i hope that helped you
 
        
             
        
        
        
There is no picture, though.
        
             
        
        
        
Answer:
Explanation:
1) Excitation brings about contraction.
2) Contraction leads to an increase in blood pressure. 
3) Changes in blood pressure results in the opening and closing of the heart valves.
4) The opening and closing of heart valves then regulates the flow of blood and it's volume.
 
        
             
        
        
        
Answer:
 Bone.
Explanation:
Calcium is one of the important element present in the body. Calcium plays an important role in the muscle contraction. The calcium ions also acts as a signalling molecule during cell signalling.
The calcium is present in our extracellular fluids, bones, and teeth. The major constituent of calcium is present in the bone. The bone consists of around 90% body;s calcium.
Thus, the correct answer is option (b).