What started the cold war?

The Cold War began after the surrender of Nazi Germany in 1945, when the uneasy alliance between the United States and Great Britain on the one hand and the Soviet Union on the other started to fall apart.Explanation:

B. The natural environment protected Egyptians from invaders and also played a  critical role in their development of agriculture and calendars.

Explanation:

The natural environment around Egypt was crucial for the development of the Egyptian civilization, due to two main reasons.

One reason is the Nile River, which was the central artery of Egypt, and crosses the territory from North to South, with a huge Delta in the extreme north. The Nile flooded the banks seasonally, leaving the soil with rich sediments that had many nutrients and that made the land more fertile. This allowed the development of agriculture, the founding of cities along the banks, and the establishment of the Ancient Egyptian Civilization.

The other reason is that this central heartland along the Nile was surrounded by deserts or by the Mediterranean Sea. This made Egypt hard to invade, and although it was invaded a few times, no invasion could ever destroy the Egyptian Civilization until the Romans, when Egypt had already more than 3 thousand years of history.