Which of the Following Is a Reason for the Discrepancy

Which of the following is a reason for the discrepancy between GDP and GDI?

A) GDP is measured from a sample of household figures while GDI is measured from tax returns filed by firms and households.
B) The sample size used to estimate these figures is very large leading to more statistical errors.
C) GDP is estimated using estimated sales provided by business while GDI is based on actual expenditures incurred by households.
D) GDP is measured from sales and inventory figures collected from a sample of business while GDI is collected from a sample of household figures.