Nile has a direct effect on the economy of Egypt as it enriches the lives of people which makes their society work.
Egypt's stability surpasses modern societies since its only source is Nile but it has given them a lot unlike modern societies which seek for several resources just to make the economy boom.
It's unending in the sense that it's the longest river, but it's an unending source because of its fertility.
Nile means "river valley" which is also the meaning of the Latin word "nilus". Egyptians call Nile, Ar which means "black" because its sedimentary gives a black hue sometimes.
I would say C) "'Oh, my poor Mathilde! But mine was imitation. It was worth at the very most five hundred francs! …'" (Paragraph 14) is the best option.
