Answer:
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium.
Explanation:
A hypothesis......Plz mark brainliest
Answer:
Number of bacteria required 
Explanation:
Given -
Size of each bacterium
micrometers long
These bacteria are arranged end to end.
The size of chain to be formed is equal to
centimetres
Let us say that in forming a chain of
centimetres nearly X number of individual bacterium are required.
hence, number of bacterium required to form
centimetres chain can be represented as

Number of bacteria required 
Differential reproduction means that some organisms in a population produce more offspring than others.
<span>
Differential reproduction refers to the difference between individuals in a population and how many offspring they are able to leave.The best adapted organisms to a given environment will leave more offspring than those who are not well adapted. Differential reproduction depends on the natural selection.</span>
Species is the most narrow category
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