Sentences of a paragraph are given below in jumbled order. Arrange the sentences in the right order to form a meaningful and coherent paragraph.

A: Its people thrived on agriculture and enjoyed a happy community life.

B: The Sumerian civilization is the oldest civilization known to mankind.

C: The term Sumer is today used to designate southern Mesopotamia.

D: Sumer used to be a flourishing urban civilization till 3000 BC.