Final answer:
The classification numbers used by importers and exporters are established by the Harmonized Tariff Schedule (HTS). Other options listed are not related to establishing these numbers. The Census Bureau compiles trade documents but does not set classifications.
Step-by-step explanation:
The classification numbers that must be used by importers and exporters are established by E) HTS, which stands for the Harmonized Tariff Schedule. The HTS is a detailed list used globally for defining product classifications in international trade. It allows for uniformity and consistency in the classification of goods and adherence to international trade agreements.
The other options listed, such as NTRB, CVD, FSC, and NTB, do not serve the function of establishing classification numbers for imports and exports. The Census Bureau, connected to foreign trade, mainly compiles a monthly record of import and export documents but does not set the classifications.