Why were so many cities able to develop between the Tigirs and Euphrates river?

I think it is the rivers were used for irrigation, which led to a food surplus (option 4) sorry if it’s incorrect

Explanation:

the federal government of the united states was established by the constitution. us is a presidential republic. the president is head of state, head of government and of a two party legislative and electoral system. the supreme court balances the powers of the federal and the state government. yhe executive branch is headed by the oresident. there are two chambers of congress, the senate and the house of representatives. judicial power is exercised by the judicial branch (or judiciary), comprised of the supreme court and lower federal courts. the judiciary's function is to interpret the   constitution as well as the federal laws and regulations.

it is a better alternative