Answer:
Rate of change of volume of the pile 
Explanation:
Given -
Rate of increase of the base of the pile
inches per minute
Height of the pile
the radius of the base
Let "h" be the height of the pile and "r" be the radius of the base.
Then 
Radius "r"
inches
Rate of change of radius i.e

Volume of conical pile

Change in volume of conical pile

Substituting the value of rate of change of radius, we get -

Rate of change of volume of the pile 
This is called a behavioral pattern. This is something deer have learned over time that gives them an advantage in the wild.
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Answer:
Use 400 x in order to study the structure clearly.
Explanation:
Cell structures could be clearly identified when magnify the microscope about 400 x by using a compound microscope. Due to high magnification power of compound microscope, the individual is able to see different structures that are present in cells. while by using lower magnification, the individual is unable to see different structures clearly. So use high magnification in order to study the cell.