Why elephants rarely get cancer is a mystery that has confused scientists for decades.

[2017·长沙模拟]Why elephants rarely get cancer is a mystery that has confused scientists for decades. A study was led by researchers at Huntsman Cancer Institute (HCI) at the University of Utah and Arizona State University, including researchers from the Ringling Bros. Center for Elephant Conservation may have found the answer. According to the results, elephants have 38 additional modified copies of a gene (基因) that encodes p53, a well­defined tumor(肿瘤) suppressor, as compared to humans, who have only two. Further， elephants may have a more powerful mechanism for killing damaged cells that are at risk for becoming cancerous. In isolated elephant cells, this activity is doubled compared to healthy human cells, and five times that of cells from patients with Li­Fraumeni Syndrome, who have only one working copy of p53 and more than a 90 percent lifetime cancer risk in children and adults. The results suggest extra p53 could explain elephants' increased resistance to cancer.
“Nature has already figured out how to prevent cancer. It's up to us to learn how different animals overcome the problem so we can adapt those strategies to prevent cancer in people，” says co­senior author Joshua Schiffman, M．D., pediatric oncologist (肿瘤学家) at Huntsman Cancer Institute, University of Utah School of Medicine, and Primary Children's Hospital.
According to Schiffman, elephants have long been considered a walking problem. Because they have 100 times as many cells as people, they should be 100 times more likely to have a cell slip into a cancerous state and cause the disease over their long life span of 50 to 70 years. And yet it's believed that elephants get cancer less often, a theory confirmed in this study. Analysis of a large database of elephant deaths estimates a cancer death rate of less than 5 percent compared to 11 to 25 percent in people.
篇章导读：本文是一篇说明文。文章讲述了通过对大象的研究，科学家得知了预防和防止癌症发生的方法。
5．Why do humans often get cancer compared to elephants according to the passage?
A．Elephants are bigger than humans.
B．Elephants have more p53 than humans.
C．Elephants are not as clever as humans.
D．Elephants eat more than humans.
答案：B　细节理解题。根据文章第一段第四句可知，答案为B。
6．Which of the following is right according to the passage?
A．Some damaged cells may be dangerous.
B．Some damaged cells are not dangerous.
C．Some damaged cells can't be cancerous.
D．Some damaged cells in elephants' bodies are more dangerous than those in humans' bodies.
答案：A　推理判断题。根据文章第一段可推知，选项A正确。本题易误选D。选项A中的dangerous和文中的“at risk for becoming cancerous”相对应。文中提及大象强有力的杀死受损细胞的能力是人的两倍，但并没有比较两者的受损细胞哪个更危险。
7．What can we know from the last paragraph?
A．Elephants have more cells than people.
B．Elephants can get cancer easily.
C．Elephants seldom die from cancer.
D．Elephants often die from cancer.
答案：C　推理判断题。从最后一段可知，大象死于癌症的百分比是比较少的，和选项C意思相近。故选C。
8．Which of the following can be the best title for the passage?
A．Elephants Help Us
B．Learn from Nature
C．How to Deal with Cancer
D．Nature Helps Us Prevent Cancer
答案：D　主旨大意题。根据文章所述，人们研究大象得知了如何预防和防止癌症发生的办法。故选D。
 
 重点单词：
1．further adv. 进一步地；而且
2．double v. (使)加倍；是……的两倍
3．resistance n. 抗拒；反对
4．span n. 跨度；范围
5．estimate v．/n. 估价；估计
重点短语：
1．at risk 有危险；冒风险  2.figure out 弄懂；弄清楚