Detailed Solution:
The correct answer is “Archaeological excavations”.
The primary source of information about the Harappan (Indus Valley) culture comes from archaeological excavations of ancient sites like Harappa, Mohenjo-Daro, and others.
These are inscriptions found in various parts of India are not related to the Harappan culture.
The Harappan civilization used seals with inscriptions, but the script remains undeciphered.