Passage 4 It’s a good idea to apply sunscreen before heading to the beach if you don’t want to bum. But for marine animals like whales，they don’t have that _1_. Species like sperm whales can spend up to six hours at the ocean’s surface in between dives, _2_ 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 _3_ 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 _4_ 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 _5_ protect their cells from UV damage. This process is _6_ 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 _7_ 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 _8_, it’s important to know what the consequences are for whales and dolphins, especially for _9_ 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 _10_ defenses to UV radiation, high exposure can still be harmful. A) similar B) diminishing C) 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 第1空答案是：