I imagine, it's A, they get a sense of the history of the area they are investigating.
Volga River is the longest river in Europe.
It is also a source of hydroelectricity for many Russian cities along its basin
Correct answer is B.
Explanation:
In their nucleus cells contain DNA. The DNA has information about size, shape and function of each cell. When the cell reaches it's full size it stops growing and starts doing whatever it's function is. If more cells are needed then the cell replicates. This explanation excludes answers A and C.
Male and female sexual cells are used to conceive a baby. These cells combine to form a new type of cells. In the first few weeks all types of cells are created. Then the creation of new types of cells stops and existing cells multiply in order to achieve needed number of cells. This explanation excludes answer D.
When we compare an adult person and a baby we can see that, for example, an adult has bigger bones than a baby. This was result of increasing number of existing types of cells without creating any new type.
