阅读下列短文，从每题所给的四个选项中，选出最佳选项。
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There are an extremely large number of ants worldwide. Each individual ant hardly weigh anything, but together they weigh almost the same as all of mankind. They also live nearly everywhere, except on frozen mountain tops or around the Antarctic. For animals their size, ants have been surprisingly successful, largely due to their wonderful social conduct.
In groups that vary in size from a few hundred to tens of millions, they organize their lives with a clear distribution of labor. Even more amazing is how they achieve this level of organization. While we use sound and sight to communicate, ants depend mostly on pheromone (信息素), which is a kind of chemical released by individuals and smelled or tasted by fellow members of a group. When an ant finds food, it produces a pheromone that will lead others straight to where the food is. When an ant comes under attack or is dying, it sends out an alarm pheromone to warn the whole group to prepare for a defensive fight.
In fact, when it comes to the art of war, ants have no equal. They are completely fearless and will take on an animal much larger than themselves, attacking in large groups and beating their target. They show so much devotion to their group that not only soldier ants but also worker ants will sacrifice their lives to help defeat an enemy.
United and devoted, these little animals have survived on the earth for more than 140 million years, far longer than dinosaurs. Because they think as one, they have a united intelligence greater than you would expect from one small individual ant.
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