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掌握了gre阅读里的长难句，到了实战演习的时候了。gre阅读练习每日一篇帮助gre考生循序渐进地进行练习和总结。希望gre考生在进行gre阅读练习时，也按着考试时候的时间规定自己的练习，这样才能有效果。 For some time scientists have believed that cholesterol plays a major role in heart disease because people with familial hypercholesterolemia , a genetic defect, have six to eight times the normal level of cholesterol in their blood and they invariably develop heart disease. These people lack cell-surface receptors for low-density lipoproteins , which are the fundamental carriers of blood cholesterol to the body cells that use cholesterol. Without an adequate number of cell-surface receptors to remove LDLs from the blood, the cholesterol-carrying LDLs remain in the blood, increasing blood cholesterol levels. Scientists also noticed that people with familial hypercholesterolemia appear to produce more LDLs than normal individuals. How, scientists wondered, could a genetic mutation that causes a slowdown in the removal of LDLs from the blood also result in an increase in the synthesis of this cholesterol-carrying protein? Since scientists could not experiment on human body tissue, their knowledge of familial hypercholesterolemia was severely limited. However, a breakthrough came in the laboratories of Yoshio Watanabe of Kobe University in Japan in 1980. Watanabe noticed that a male rabbit in his colony had ten times the normal concentration of cholesterol in its blood. By appropriate breeding, Watanabe obtained a strain of rabbits that had very high cholesterol levels. These rabbits spontaneously developed heart disease. To his surprise, Watanabe further found that the rabbits, like humans with familial hypercholesterolemia, lacked LDL receptors. Thus, scientists could study these Watanabe rabbits to gain a better understanding of familial hypercholesterolemia in humans. | 
