Answer:
The correct answer will be option-D.
Explanation:
Calcium plays an important role in muscle contraction as they are released from the sarcoplasmic reticulum after they receive electric impulse.
Calcium triggers the muscle contraction cycle as these calcium ions bind to the troponin-tropomyosin complex. This binding exposes the myosin-binding site on the actin on which high energy myosin binds and cross-bridge is formed.
This cross-bridge formation causes the contraction of the sarcomere and therefore muscle contracts.
Thus, option-D is the correct answer.
 
        
             
        
        
        
Answer:
hey you didn't provide the complete question. what's the full question maybe I could help
 
        
             
        
        
        
Answer:
The Amazon is a critical absorber of carbon of carbon dioxide, a greenhouse gas produced by burning fossil fuels, like oil and coal. ... The Amazon absorbs 2 billion tons of CO2 per year (or 5% of annual emissions), making it a vital part of preventing climate change.
Explanation:
 
        
             
        
        
        
<u>Answer:</u>
An example situation of artificial selection is "More African elephants today naturally lack tusks compared to the elephant populations 100 years ago, because big game hunters sought elephants for ivory".
<u>Explanation:</u> 
- The process of breeding animals to acquire the desired characteristics by the external means other than natural selection and behavior of animal itself is called as artificial selection. 
- The first artificial selection was carried out by Darwin when he mated penguins that would have a higher chance of breeding. 
- The practice of artificial selection was existing in human civilization a long time ago. 
- This process was used to use wild animals and domestic animals in battles and other household works.