Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 42 to 46. 

     There is (42) _______ debate between archeologists about when and where the first civilizations developed. That is because the answer to that question depends on what one defines as a civilization. If a civilization is simply a small group of people having a similar culture and beliefs, then civilizations have existed in many parts of the world for thousands of years. If a civilization is defined as a larger, more complex society (43) _______ a government and the construction of cities, then the first civilization was probably the Sumerian civilization in what is now Iraq. The Sumerians were (44) _______ from the Ubaid culture, which was made up of small villages of farmers who lived slightly farther north. Sometime around 4,000 B.C. these farmers moved down into the valley along the Tigris River. 

     This land received little rain, and was unsuitable for farming. Therefore, it was empty and the Sumerians had plenty of (45) _______ and little competition from other peoples. What allowed the Sumerians to successfully farm in this dry land was their knowledge of irrigation, the practice of taking water from a river or lake and moving it to fields through the use of man-made canals. This allowed the Sumerians to farm here successfully (46) _______ the lack of rain. We know that the Sumerians had a great understanding of irrigation because their language is filled with words related to it.