Which of the following is one of the five causes of a business cycle?
a. decrease in consumer demand
c. recession
b. external shocks
d. none of the above

A recession is one of the five causes of a business cycle. 
Business cycles are measured by looking at the growth rate of the gross domestic product of a country. There are five causes of a business cycle:
1. Changes in interest rates2. Changes in house prices3. Changes in consumer and business confidence 4. The local or world economy moves into a recession5. The local or world economy moves out of a recession. 
These causes can also be seen as unstable fluctuations rather than stable cycles. 

The awnser is b i believe