1.Indiscriminately dumping of waste materials and inadequate sewage treatment are two serious causes of environmental pollution.





2.The builders of the variety ancient cliff ruins scattered throughout the canyons and mesas of the arid Southwest of the United States are known as the cliff dwellers.





3.A fragrant plant has tiny sacs that makes and stores the substances that give it a pleasant odor.





4.Nomadic hunter and gatherer societies have access to only a limited amount of food in an area and moved on when they have exhausted each locality .





5.Collagen, a strong rubbery protein, supports the earflaps and the tip of nose in humans .





6.The outer layer of the heart, called the pericardium, forms a sac in what the heart lies.





7.Wood from the ash tree becomes extremely flexibly when it is exposed to steam.





8.The ability to talk is one of the skill that make humans different from the rest of the animal world .





9.In plane geometry, the sum of the internal angles of any triangle has always equal to 180 degrees.





10.Polar bears are bowlegged and pigeon-toed, adaptations that enable this massive animals to maintain their balance as they walk .