In an Economy Consisting of Only Households and Firms,how Can

In an economy consisting of only households and firms,how can GDP be computed?

A) by adding up the total expenditures of households and subtracting savings
B) by adding up the income paid by firms only in exchange for labour
C) by adding up either total income paid by firms or total expenditures of households, but not both
D) by adding up both the total expenditures of households and the total income paid by firms