Why does GDP equal aggregate income and also equal aggregate expenditure?

GDP equals aggregate income and also equals aggregate expenditure because $q,.$

A$.$ labor produces final goods and all purchases in the economy are purchases of final goods

B$.$ aggregate income measures profit as net profit and aggregate expenditure measures investment as net investment

C$.$ the Department of Commerce has defined GDP in such a way that it can be calculated by either summing total income or by summing total expenditures

D$.$ firms pay out as incomes $($aggregate income$)$ everything they receive from the sale of their output $($aggregate expenditure$)$