Sentence Correction (SC) | Re: Excavators at the Indus Valley site of Harappa in eastern

Excavators at the Indus Valley site of Harappa in eastern Pakistan say the discovery of inscribed shards dating to circa 2800 - 2600 B.C.indicate their development of a Harappan writing system, the use of inscribed seals impressed into clay for marking ownership, and the standardization of weights for trade or taxation occurred many decades, if not centuries, earlier than was previously believed.

a) indicate their development of a Harappan writing system, the use of
b) indicate