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- Mental and physical deterioration both occur naturally with age. 随着年龄的增长，心智和体力自然衰退。
- Much higher and lower densities also occur naturally. 树木的适应范围这麽广，这点值得特别注意。
- The required abzymes occur naturally in patients with lupus. 在狼疮病人的体内，能自然生成所需要的该种分离酵素。
- The pig is the only animal in which hog cholera is known to occur naturally. 猪是已知自然发生猪瘟的唯一动物。
- Sugar occurs naturally in fruit. 水果天然含糖分。
- Such chemicals occur naturally in the body and in fruits and vegetables and are believed to neutralize free radicals. 这类化学物质在人体内与水果蔬菜中会自然产生，而且据信可以中和自由基。
- Salt occurs naturally in sea water. 盐天然存于海水中。
- Emulsifying agents occur naturally in many animal substances including egg yolks and milk. 自然界中,很多动物体中含有乳化剂,如蛋黄和牛奶。
- Pure crystalline boron is a black, lustrous, very hard but brittle semiconductor that does not occur naturally. 纯晶态硼为黑色有光泽的半导体，硬度很高。
- Hydrates occur naturally in pipelines, and are unpopular because they clog the flow of oil. 水合物可以在输油管道中自然形成，因为它们阻碍石油的流动，因而不受欢迎。
- Stained teeth can occur naturally as we age, but some common foods, drinks, and even mouthwashes can cause teeth stains. 当然，随着年龄的增长，牙齿会逐渐产生色斑，但一些常见的食物，饮料甚至漱口水都可能导致牙齿色斑。
- It's worth remembering that long hair of the thick, glossy, swishy variety is incredibly rare, and doesn't often occur naturally in the wild. 我们要记着,一头浓密光泽、唰唰作响的长发是非常难得的,而且通常不是天生的。
- It is natural for a cat to catch mice. 猫捉老鼠是本能。
- While landslides can occur naturally, scientists say there is unmistakable evidence that Yamal’s ancient permafrost is melting. 尽管山体滑坡也会自然发生。但是，科学家却表示，有确凿的证据表明，古老的雅马尔永久冻土层正在融化。
- It's natural to slack2 off towards the end of a hard day's work. 一天紧张工作快结束的时候有些放松是自然的。
- Although wolf hybrids can occur naturally in the wild, this happens very infrequently due to the territorial nature of the wolf. 虽然狼混血儿能自然地在荒野中生存，但是这很少发生在野外的狼的领土。
- Many natural materials are becoming scarce. 许多天然原料越来越少。
- And in particular, it's to do with chemicals called phenolics that occur naturally in the skins of fruit, vegetables and herbs. 特别是一种叫做"酚"的化学品在起作用。它存在在水果的果皮、蔬菜和草药中。
- Known as conjugated linoleic acids (CLAs), some of these trans fats occur naturally in dairy products and meat, especially milk and butter. 学名叫作共轭亚油酸（CLAs），一些反式脂肪自然存在于乳制品及肉类中，特别是牛奶和黄油。
- Chromosome mutations can occur naturally but their frequency is increased by the effect of x-rays and chemical mutagens. 染色体的突变是自然发生的，但通过X射线或化学诱变剂可以增加突变的频率。
