The sumerians were among the first civilizations to develop a calendar based on the movement of the stars in the sky. why was a calendar important to the sumerians?
select one:
a. so they knew when the rivers were going to flood.
b. so they could tell when the trees were going to change colors.
c. so they knew when to expect traders from other civilizations.
d. so they knew when to make offerings to their gods.

The answer is,

a. So they knew when the rivers were going to flood,

because Mesopotamian civilization was built upon the "twin rivers" (the Euphrates and Tigris Rivers). When the rivers flood, the water would leave behind fertile soil (excellent for farming) when levels returned to normal, washing up minerals collected as the river followed its normal course of movement.

the dissolution of the soviet union[a] occurred on december 26, 1991, officially granting self-governing independence to the republics of the soviet union. it was a result of the declaration number 142-н of the supreme soviet of the soviet union.[1] the declaration acknowledged the independence of the former soviet republics and created the commonwealth of independent states (cis), although five of the signatories ratified it much later or did not do so at all. on the previous day, december 25, soviet president mikhail gorbachev, the eighth and final leader of the soviet union, resigned, declared his office extinct, and handed over its powers – including control of the soviet nuclear missile launching codes – to russian president boris yeltsin. that evening at 7: 32 p.m., the soviet flag was lowered from the kremlin for the last time and replaced with the pre-revolutionary russian flag.[2]

previously, from august to december, all the individual republics, including russia itself, had either seceded from the union or at the very least denounced the treaty on the creation of the ussr. the week before formal dissolution, 11 republics signed the alma-ata protocol formally establishing the cis and declaring that the ussr had ceased to exist.[3][4] both the revolutions of 1989 and the dissolution of the ussr also marked the end of the cold war.

several of the former soviet republics have retained close links with the russian federation and formed multilateral organizations such as the commonwealth of independent states, eurasian economic community, the union state, the eurasian customs union, and the eurasian economic union to enhance economic and security cooperation. on the other hand, the baltic states have joined nato and th