The correct option is C The Harappan civilisation made use of only one symbol on their seals.
Trade has been an important factor in historians establishing possible relations between civilisations. Seals from either civilisation, in this case, have been found in sites belonging to the other. The Harappans are said to have made use of boats on their overseas trade trips and brought back gold and silver from Oman and Persia, respectively. More than 2,000 varieties of seals have been found at the various Harappan sites.