Question

1. one of the great achievements of the indus valley civilization was

its sophisticated plumbing and sewage system
the invention of the chariot
iron technology
its number system

Explanation:

The Indus Valley civilization is known for its advanced urban planning, including a sophisticated plumbing and sewage system (e.g., in cities like Mohenjo - Daro and Harappa). The invention of the chariot is associated with other civilizations, iron technology was more prominent in later periods, and their number system, while notable, is not as defining an achievement as the plumbing/sewage system. So the correct option is the one about the sophisticated plumbing and sewage system.

Answer:

A. its sophisticated plumbing and sewage system