It's a good thing sloths don't have to go to school. They'd never make it on time. These drowsy tree-dwellers sleep up to 20 hours a day! And even when they are awake, they barely move at all. In fact, they're so incredibly sluggish, algae actually grows on their fur.
幸好樹懶不用上學，因為它們永遠不會準時到校。這些昏昏欲睡的樹懶每天要睡20個小時！即使它們醒著，也幾乎不動。事實上，樹懶行動緩慢到連它們的皮毛上都長出了水藻。
Sloths live in the tropical forests of Central and South America. With their long arms and shaggy fur, they resemble monkeys, but they are actually related to armadillos and anteaters. They can be 2 to 2.5 feet (0.6 to 0.8 meters) long and, depending on species, weigh from 8 to 17 pounds (3.6 to 7.7 kilograms).
樹懶生活在中美洲和南美洲的熱帶森林中。樹懶的長臂和毛茸茸的皮毛像猴子一樣，但它們實際上與犰狳和食蟻獸同種。樹懶體長2至2.5英尺（0.6至0.8米），根據物種的不同，重量可達8至17磅（3.6至7.7公斤）。
There are two main species of sloth, identified by whether they have two or three claws on their front feet. The two species are quite similar in appearance, with roundish heads, sad-looking eyes, tiny ears, and stubby tails. Two-toed sloths are slightly bigger and tend to spend more time hanging upside-down than their three-toed cousins, who will often sit upright in the fork of a tree branch. Three-toed sloths have facial coloring that makes them look like they're always smiling. They also have two extra neck vertebrae that allow them to turn their heads almost all the way around!
樹懶主要有兩種，可以通過它們的前腳有兩個或三個爪來區分。這兩個物種在外觀上非常相似，圓圓的頭，憂傷的眼睛，小小的耳朵，尾巴粗短。兩趾樹懶稍微大一點，比三趾表兄弟更多時間倒掛在樹上，三趾樹懶經常坐在樹叉裡。三趾樹懶面部有顏色，看起來總是微笑的樣子。它們還有兩個額外的頸椎，可以讓腦袋幾乎360度轉過來！
Some scientists think sloths developed their slow-motion lifestyle so they would be less noticeable to predators such as hawks and cats, which rely heavily on their eyesight when hunting. The algae that grows on sloths' fur also helps them avoid predators by letting them blend in with green leaves.
一些科學家認為樹懶之所以行動如此緩慢，是為了讓鷹類和貓類之類的食肉動物不注意到自己，這些食肉動物在捕獵時主要依賴於它們的視力。生長在樹懶毛皮上的藻類也可以幫助它們避開食肉動物。
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