Answer:A. The release of calcium ions causes myosin and actin to attach to each other.
The contraction of skeletal muscles takes place by induction of a nerve impulse, which produces a movement and the interaction of the filaments containing proteins named as actin and myosin. This interaction of filaments is regulated by proteins  called tropomyosin and troponin present on the actin filaments. The motor nerve causes the depolarization of the muscle membrane sarcolemma. This triggers the sarcoplasmic reticulum to release calcium ions. This calcium binds to troponin and thus allows the tropomyosine strand on the actin filament to displace so that the part of the actin where myosine head needs to be attached remain uncovered. Binding of the actin myosine filament results in contraction. 
Hence, the release of calcium ions causes myosin and actin to attach to each other causes muscle contraction. 
 
        
             
        
        
        
It prevents water evaporation.
100% correct
 
        
                    
             
        
        
        
Answer:
glucose & fructose
Explanation:
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A diet deficient in calcium can cause osteopenia. The deficiency of calcium may Cause a low bone density which is a condition caused in osteoporosis. Hence the correct answer is B osteopenia.