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  3. It’s a good idea to apply sunscreen before heading to the beach if you don’t want to burn. But for marine animals like whales, t

It’s a good idea to apply sunscreen before heading to the beach if you don’t want to burn. But for marine animals like whales, t

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问题     It’s a good idea to apply sunscreen before heading to the beach if you don’t want to burn. But for marine animals like whales, they don’t have that【C1】______Species like sperm whales can spend up to six hours at the ocean’s surface in between dives,【C2】______in the sunlight. So how do they protect themselves from a serious case of sunburn?
    It turns out that their bodies have a similar defense【C3】______against the sun’s UV radiation as people. Blue whales—which have the lightest skin color of the three species—tan during their summer stay before【C4】______, back to their northern feeding grounds. Sperm whales don’t tan. They can receive an "overdose" of UV radiation during their hours at the ocean’s surface, and they have proteins that【C5】______protect their cells from UV damage. This process is【C6】______to how human bodies produce antioxidants in response to molecules that can cause a lot of genetic and cellular damage. And fin whales escape sun damage thanks to their high levels of melanin—a dark substance in the skin to protect humans from UV radiation.
    Older whales and whales with less【C7】______of melanin in their skin—like blue whales—had the greatest level of damage in their mtDNA. Fin whales, which had the greatest amount of melanin, had the least amount of mtDNA damage.
    Now that the ozone layer that shields Earth from UV radiation is gradually【C8】______it’s important to know what the consequences are for whales and dolphins, especially for【C9】______or endangered species. Although it’s difficult to tell what causes many of these skin conditions, UV damage is one cause. Even though whales have【C10】______defenses to UV radiation, high exposure can still be harmful.
    A)similar B)diminishing G)liability D)migrating
    E)mutual F)mechanism G)effectively H)jerking
    I)instantaneously J)vulnerable K)content L)baking
    M)inherent N)perspective O)option
【C4】
选项
答案D
解析 空格前的before是介词，而空格后紧跟表方位的back to…，可见此处应该选用动词的现在分词，表明鲸鱼在度过了夏天之后的“动向”。动词库中的migrating一词最为恰当，填入文中表示“迁徙到北方去觅食”。
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