Cairo, the capital of Egypt, is situated on the Nile River - the longest river in the world and the lifeblood of Egypt. The Nile has sustained Egyptian civilization for thousands of years. The Tigris (Option C) flows through Iraq and Turkey, while Livingstone (Option A) appears to be a person's name (David Livingstone). 'Thems' (Option D) is likely a typo for 'Thames', which flows through London.