One of the greatest achievements of the Maya civilization was ​

Their system of mathematics.

Explanation:

The Maya discovered zero.  Most of the world's civilizations had no concept of zero at the time of the Mayans.  Without zero there would be: No algebra, no arithmetic, no decimal, no accounts, no physical quantity to measure, no boundary between negative and positive numbers, and no computers.  The Mayan’s discovery of zero was one of the most significant steps to get to where we are today.

The counting system was so simple.  The Mayans figured out a genius system of counting which only required three symbols, a dot, a line, and a shell.  These three symbols could be used in various combinations to keep track of the calendar and do arithmetic.  Even the most uneducated people could use it to do basic trade.

president franklin roosevelt supported the tva as part of his first new deal measures approved by congress in 1933. this new agency was designed to control floods, produce electric power, and improve the lives of people living in the tennessee valley. the tva accomplished many of these goals despite problems.

it's lower nubia : ) good luck