The correct answer is: a) Carnelian
Carnelian is a type of chalcedony that is prized for its deep red color. It was widely used in Harappan jewelry and other decorative objects. The Harappans traded carnelian with other cultures throughout the Indus Valley and beyond.
Gold, copper, and ivory were also traded by the Harappans, but they were not as important as carnelian. Gold was used to make jewelry and other objects for the elite, while copper was used to make tools and weapons. Ivory was used to make carvings and other decorative objects.
The Harappans were a Bronze Age civilization that flourished in the Indus Valley from about 2600 to 1900 BCE. They were skilled in agriculture, metalworking, and pottery. They also built a complex system of cities and towns. The Harappan civilization declined around 1900 BCE, and its cause is still unknown.