(C) West Asia
As early as 3000 BCE, an active coastal trade linked the Indus Valley Civilisation with present-day West Asia.
The answer is directly stated in the passage from Chapter 3 ("The Pre-modern World"): "As early as 3000 BCE an active coastal trade linked the Indus valley civilisations with present-day West Asia." Students must read source passages carefully; the other options (North America, South America, South Australia) have no connection to ancient Indus trade routes.