Which of the following statements is (are) true?
a. short-run average total cost curves intersect the long-run average total cost curve at its minimum point.
b. the long-run average total cost curve is derived by tracing out all of the firm's short-run average total cost curves.
c. the long-run average total cost curve indicates that it is more costly to produce output in the long run, especially when input prices are rising because of inflation.
d. it is not possible for two short-run average total cost curves to cross.

The business cycle is the periodic but irregular up-and-down movement in economic activity, measured by fluctuations in real gross domestic product (gdp) and other macroeconomic variables. a business cycle is typically characterized by four phases—recession, recovery, growth, and decline—that repeat themselves over time. economists note, however, that complete business cycles vary in length. the duration of business cycles can be anywhere from about two to twelve years, with most cycles averaging six years in length. some business analysts use the business cycle model and terminology to study and explain fluctuations in business inventory and other individual elements of corporate operations. but the term "business cycle" is still primarily associated with larger (industry-wide, regional, national, or even international) business trends.