Which of the following statements best describe how economists calculate GDP? a. Economists at the Congressional Budget Office calculate GDP for a given year by adjusting the previous year's GDP with inflation. b. Economists at the Census bureau collect data from surveys sent to consumers, private firms and government agencies and add them up on a yearly basis. c. Economists at the Bureau of Economic Analysis pull together data on sales, imports, exports, government purchase and investments from various government sources every 3 months. d. Economists at the Bureau of Labor Statistics collect data from surveys sent to consumers, private firms and government agencies and add them up every 3 months