Answer:
Indus River -Civilization
writing on stone seals-Key Features of the Indus Valley
cities of Harappa and Mohenjo Daro -Civilization
disappearance of people living in cities over time - Mysteries of the Indus Valley
Explanation:
Indus river civilization has a long mystery behind it, And the correct match for this question is as mentioned above. Disappearance is most mysterious, and I would like to keep it secret, but it is to encourage you to read the whole story. And it's much like the history of Constantinople or present-day Istanbul. Please do have a read. You will love these histories.