Answer:
a. The Decimal System
Step-by-step explanation:
The Decimal System, is one of the great mathematical innovation form ancient India. There is no clear date and place about the invention the decimal system.
It was first recorded in India, then spread to Islamic world, and further to Europe. Decimal system gave a unique turn to the world of mathematics and made the counting or measurement easy.
Hence, the correct answer is "a. The Decimal System".