The Statistical Discrepancy in a Country's Balance of Payments Is

The statistical discrepancy in a country's balance of payments is never zero because:

A) individuals and firms engaged in international transactions are not required to report every detail of their activities, and therefore they don't.
B) the customs service only spot checks imports and exports.
C) many indirect estimates of payments flows are used, and they are not very accurate.
D) All of the above.
E) None of the above.