Which river valley civilization is considered to have been the first to use geometry and the first to create a solar calendar?

Relatively steep zone that is compared with the shelf that marks the boundary between continental crust and ocean crust.

Simple astronomical telescope the objective lens has a focal length of 75 cm and that of a piece of 5cm of the lenses are 18 cm apart when will be final image of a distant object before

What was on result of the potato famine