What was unique about the Indus Valley settlements?

The ruins of two ancient cities, Harappa and Mohenjo-Daro (both in modern-day Pakistan), and the remnants of many other settlements, have revealed great clues to this mystery. Harappa was, in fact, such a rich discovery that the Indus Valley Civilization is also called the Harappan civilization.

Many scholars believe that the collapse of the Indus Valley Civilization was caused by climate change. Some experts believe the drying of the Saraswati River, which began around 1900 BCE, was the main cause for climate change, while others conclude that a great flood struck the area.

The remains of the Indus Valley Civilization cities indicate remarkable organization; there were well-ordered wastewater drainage and trash collection systems, and possibly even public granaries and baths. Most city-dwellers were artisans and merchants grouped together in distinct neighborhoods.

The sun's parallax would be 180 degrees, greater than which you can't get.  so a. would be your anwser 

Ithink the answer to that would be b):