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  3. Sexual Reproduction Birds do it. Bees do it. But dandelions don’t. The prodigious spread of these winsome weeds underscores a

Sexual Reproduction Birds do it. Bees do it. But dandelions don’t. The prodigious spread of these winsome weeds underscores a

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问题                            Sexual Reproduction
   Birds do it. Bees do it. But dandelions don’t. The prodigious spread of these winsome weeds underscores a little-appreciated biological fact. Contrary to human experience, sex is not essential to reproduction. Asexual organisms can often churn out multiple generations of clones, gaining a distinct edge in the evolutionary numbers game. And therein lies the puzzle: If sex is such an inefficient way to reproduce, why is it so widespread?
   Sex almost certainly originated nearly 3. 5 billion years ago as a mechanism for repairing the DNA of bacteria. Because ancient earth was such a violent place, the genes of these unicellular organisms would have been frequently damaged by intense heat and ultraviolet radiation. " Conjugation" — the intricate process in which one bacterium infuses genetic material into another — provided an ingenious, if cumbersome, solution to this problem, although bacteria continued to rely on asexual reproduction to increase their numbers.
   Animal sex, however, is a more recent invention. Biologist Lynn Margulis of the University of Massachusetts at Amherst believes the evolutionary roots of egg and sperm cells can be traced back to a group of organisms known as rotests that first appeared some 1. 5 billion years ago.(Modern examples include protozoa, giant kelp and malaria parasite. ) During periods of starvation, Margulis conjectures, one rotest was driven to devour another. Sometimes this cannibalistic meal was incompletely digested, and the nuclei of prey and predator fused. By joining forces, the fused cells were better able to survive adversity, and because they survived, their penchant for union was passed on to their distant descendants.
   From this vantage point, human sexuality seems little more than a wondrous accident, born of a kind of original sin among protozoa. Most population biologists, however, believe sex was maintained over evolutionary time because it somehow enhanced survival. The mixing and matching of parental genes, they argue, provide organisms with a novel mechanism for generating genetically different offspring, thereby increasing the odds that their progeny could exploit new niches in a changing environment and, by virtue of their diversity, have a better chance of surviving the assaults of bacteria and other tiny germs that rapidly evolve tricks for eluding their hosts’ defenses.
By "a little-appreciated biological fact" , the author means______.
选项 A、most people are not familiar with the reproduction of dandelions
B、most people are not familiar with asexual reproduction
C、sexual reproduction is seldom favored by biologists
D、asexual reproduction is seldom favored by biologists
答案B
解析 句子主旨题型，答案是B。本题考查对文中特定句子主旨的理解。考查句在词汇理解层面存在两个关键点：一是appreciate一词，该词为大家所熟悉的义项是“感激，欣赏”，而此句适合的义项则是“知晓，领会”，整句可直译为“一个鲜为人知的生物学事实”，C、D选项将appreciate错误理解为favor，将biological一词错误理解为“生物学家的”，故先排除；二是fact一词，该词行使的是指代功能，此句本身未说明所指，故需联系上下文加以理解。从冠词a一词可判断此概念在文中属于首次提及，可推知具体的阐释会出现在此句之前而非之后，而A选项“蒲公英的繁衍”出现在该句之前，为作者所要陈述事实的证据，故排除。紧随其后的“Contrary to human experience，sex is not essential to reproduction．”一句对考查句进一步加以解释说明，可见大多数人认为性对于繁衍而言是必要条件，由此推定C选项“大多数人对无性繁衍不熟悉”符合作者的表意主旨。本题核心：留意常见词汇的特殊义项，同时善于运用语法知识锁定正确的信息点所在。
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