Why does the average variable costs curve first rise, then fall? Why is it shaped like a "U"?

The Average
Variable Cost Curve represents the correlation between the average cost a business incurs for a
product and the quantity of the product produced. The initial rising and subsequent falling of
the Average Variable Cost Curve can be reflected in three phases. The first phase reflects the
increase in returns and decrease in costs. This means that small quantities of the product are
being produced at increased prices. The second phase involves the constant returns to the
variable factors. The third...

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