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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
【C3】
选项
答案F
解析 虽然空格前的defense是名词，但从句宾语部分意思仍未完整，因此空格应该还是名词，被defense修饰作句子宾语。此处应选mechanism，表明鲸鱼自身拥有防晒的“保护机制”。
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