Which one of following is ''one of the oldest ancient civilizations''?

Extending from modern day Afghanistan and Pakistan to northwest India, the Indus Valley Civilization covered 1.25 million kilometers, making it the most widespread civilization of the ancient world. The earliest people gathered around the basin of the Indus River, establishing farming settlements. 3300 BCE is when historians generally clock the first signs of urbanization. By 2500 BCE, the Indus Valley Civilization was thriving, its people living in dozens of highly developed and spacious urban centers. There is even evidence that houses had individual bathrooms that led to a sophisticated underground sewage system.

The local people had a writing system. They were also great mathematicians. But what is more astounding is that archaeologists have found no traces of warfare or mass violence. It is estimated that they lived without armor and weapons for more than 700 years. Instead, they were a peaceful people who traded amicably with neighboring civilizations. It is perhaps this disinterest in war that led to their downfall at the hands of Central Asian invaders. Other historians, however, claim their end was due to a great flood.