1. 1st century BC The water harvesting system that taps the flood waters of the Ganga River was at Shringaverapura, located in the present-day Allahabad district of Uttar Pradesh state of India.

2. The system was composed of three percolation-cum-storage tanks, fed by an 11-meter wide and 5-meter deep canal, which diverted flood water from the monsoon-swollen Ganga.

3. During the reign of Chandragupta Maurya, large-scale dams, irrigation systems and harvesting systems were constructed throughout his kingdom.

The correct answer is SIMA. It is also known as the 'mantle' and is the second layer of the Earth's three concentric layers, the other two being SIAL (crust) and NIFE (core). The major constituent elements of SIMA (second layer) are magnesium and silicon.