The correct answer is option 'B', Proto-Historical period.

Explanation:
The Indus Valley Civilization, also known as the Harappan Civilization, was an ancient urban civilization that thrived in the Indus River valley, in present-day Pakistan and northwest India, from about 3300 BCE to 1300 BCE.

Proto-Historical period:
The term "Proto-Historical" refers to a period in history that lies between prehistoric and historical times. It is a transitional phase when societies began to develop writing systems, but the written records are limited or not fully deciphered.

Indus Valley Civilization:
The Indus Valley Civilization is considered one of the world's earliest urban civilizations. It was a highly advanced and sophisticated society that had well-planned cities, advanced agriculture, and a system of writing. However, the script used by the Indus people has not yet been deciphered, which makes it difficult to fully understand their history and culture.

Key features of the Indus Valley Civilization:
1. Urban planning: The cities of the Indus Valley Civilization were meticulously planned, with grid-like street patterns, well-organized houses, and sophisticated drainage systems.
2. Agriculture and trade: The Indus people were skilled farmers who cultivated a variety of crops, including wheat, barley, and cotton. They also engaged in long-distance trade, as evidenced by the discovery of seals and artifacts from distant regions.
3. Art and craftsmanship: The Indus Valley Civilization produced exquisite pottery, jewelry, and figurines. They displayed a high level of craftsmanship and artistic skill.
4. Religion and spirituality: The people of the Indus Valley Civilization practiced various religious and spiritual beliefs. The discovery of seals with animal motifs and the presence of ritual baths and fire altars suggest a complex religious system.
5. Decline and disappearance: The exact reasons for the decline of the Indus Valley Civilization are still debated among historians. Some theories suggest that environmental factors, such as climate change or a shift in the course of the Indus River, may have contributed to its decline.

Conclusion:
The Indus Valley Civilization belongs to the Proto-Historical period because it existed during a time when writing systems were developing, but the written records of the civilization have not been fully deciphered. It is a fascinating period in history that continues to intrigue archaeologists and historians, providing valuable insights into the early development of human civilization.

The term proto history, in this context, refers to the transition period between the advent of literacy and the writings of the earliest historians. Harappans knew writing but their script remains undeciphered and thus their culture has been termed as proto historical.