What are the essential 4 parts for a civilization to develop? explain how rivers
were the source of civilization?

One of the things that is important for a civilization to develop is a good geographic location, which is why most early civilizations were located near rivers, thus you have river valley civilizations because it had rich soil, good for planting, growing crops. Eventually many of the people starting living in permanent settlements (neolithic revolution). Rivers also brought monsoons, but also brought many floods. Many developed irrigation systems and canals, and made many other things.

Aparagraph should contain a topic, a subject that will be a focused in the whole composition of the writing. to understand better, in the paragraph, a brief discussion of examples related to the topic should be discussed briefly. a complete paragraph must have an introductory part, a body, and a conclusion. 

a paragraph must have a unity especially the words used, it should not confuse the reader. there should be coherence in the subject being discussed. a topic sentence must be followed. most importantly, an adequate development in the structure from the beginning until to the conclusion.