The correct answer is Trading.

Tertiary Sector:

• The sector that helps in the development of the Primary and Secondary sectors through providing services.
• Transport, communication, banking, storage, trade, etc. all come under the tertiary or service sector. 
• However, it also includes services that don’t help directly in producing goods. 
• E.g. education, healthcare, information technologies, network operators, etc.

Primary Sector

• Primary Sector: the sector that includes natural products like agricultural goods (rice, wheat, cotton, etc.) produced by exploiting the natural resources of the earth.
• Dairy, fishing, forestry and minerals, and ores are also natural products and therefore activities involved in attaining those products also fall under the primary sector.

Secondary Sector

• Secondary Sector: the sector that includes goods that are transformed from natural products through industrial activities or manufacturing.
• It includes artificial techniques which change the form of natural products.
• E.g.: making clothes using cotton fiber from the plant. It is also called the Industrial Sector.