18．Great white sharks，the world's largest predatory（食肉的）fish，eat three to four times more food than previously thought，an Australian study shows．
The U．S．research from the 1980s estimated a meal of 30 kilograms could make a one-ton shark continue living for more than six weeks．
That made assumptions that large sharks could survive long periods without eating．
However，a University of Tasmania-led study published this week in Scientific Reports found that 30 kg was only enough for 12-15 days．
Researchers tagged （给…附上标签）a dozen great white sharks at Neptune Islands off South Australia and calculated their metabolic（新陈代谢的）rate based on swimming speeds．They worked out how much energy the sharks burned and how much food they required．
"Their metabolic rate is faster than we assumed．"
Jayson Semmens was the lead author on the study．He said，"They（U．S．researchers） picked a shark that probably wasn't working very hard at the time when they did it．At the time it was a new study．They did some metabolic work similar to us but on one shark．"
"The white sharks，which we tagged，are working pretty hard…they're coming up to some pretty high speed to catch the seals．"he said，"Their metabolic rate is much faster than what we had assumed．These animals are probably going to be feeding every day，rather than several weeks．"
The research also sought to improve understanding of how sharks fit into the ocean ecosystem．
"We don't have a good handle on the population sizes of white sharks．We know that sharks in general are under pressure around the world from overfishing，"Semmens said，"Furthermore，they're long-lived，they reproduce late in their life and they produce a small number of babies．"
Semmens said the effects of removing white sharks from the ocean were thus far more important than realized．"They're keeping under control a lot more animals than we thought，"he said．
51．The U．S．research made people believe thatD．
A．large sharks could live without eating meat
B．sharks gained several kilograms in six weeks
C．a one-ton shark needed to eat 30 kg every meal
D．large sharks could live without eating for several weeks
52．What is Semmens'attitude towards U．S．researchers'job？C
A．Uninterested
B．Surprised
C．Objective
D．Satisfied
53．The shades'metabolic rate calculated by the two research groups is different probablyD
A．they used different research methods
B．they studied sharks of different sizes
C．the sharks they used for research were of different species
D．the sharks they used for research swam at different speeds
54．What do you know about white sharks？A
A．They play an important role in ocean ecosystem．
B．They can produce a large number of babies
C．They swim more slowly than seals．
D．They live a short life．
55．The author's purpose of writing the text is most likely toD
A．entertain
B．persuade
C．describe
D．inform．
分析 之前研究认为大白鲨吃一顿三十公斤的大餐可以持续存活六个多星期，但是现在的一项研究表明它们的饮食量比之前认为的要大三到四倍，而且该研究还试图提高对于大白鲨是如何适应海洋生态环境的理解．
解答 51--55DCDAD
51．答案：D 考查细节推理，根据文章第二段的"The U．S．research from the 1980s estimated a meal of 30 kilograms could make a one-ton shark continue living for more than six weeks．"（20世纪80年代的美国研究估计一顿30公斤的大餐能够使一头一吨重的鲨鱼持续存活六周以上）可知本题答案为D选项．
52．答案：C 考查细节推理，根据文章中的He said，"They （U．S．researchers） picked a shark that probably wasn't working very hard at the time when they did it．At the time it was a new study．They did some metabolic work similar to us but on one shark．"（他说，"美国研究者选了一头有可能它们做研究时工作并不是很努力的鲨鱼，那时候它还是一个新的研究．他们做了一些与我们类似的新陈代谢的研究，但是只对一头鲨鱼做的．"）可知 Semmens对于美国研究者所做的工作的态度是"客观的"（陈述的都是事实），故本题答案为C选项．
53．答案：D 考查细节推理，根据文章第五段的"…calculated their metabolic （新陈代谢的）rate based on swimming speeds"（根据它们的游泳速度来计算它们的新陈代谢率）可知本题答案为D选项．
54．答案：A 考查细节推理，根据文章倒数第三段的"The research also sought to improve understanding of how sharks fit into the ocean ecosystem"（该研究也寻求提高对于鲨鱼是如何适应海洋生态系统的理解）及最后一段的"Semmens said the effects of removing white sharks from the ocean were thus far more important than realized"（Semmens说从海洋中把鲨鱼移除掉的影响远比我们意识到的要重大）可知本题答案为A选项．
55．答案：D 考查文章理解，本文主要讲了最新的一项研究表明大白鲨的饮食量比之前研究所认为的要多几倍以及大白鲨是如何适应海洋生态环境的，故此文的目的属于"告知"．
点评 本文是一篇科普类阅读，题目涉及多道细节理解题，做题时结合原文和题目有针对 性找出相关语句进行仔细分析，结合选项选出正确答案．推理判断也是要在抓住关键句子的基础上合理的分析才能得出正确的答案．
