Questions 24 to 27 are based on the following passage.
Humans have long turned to the dog for its nose, especially in its ability to hunt, track missing people, and search for drugs- But there is a new challenge： Bomb-detecting dogs now have to learn to find the increasingly common Improvised Explosive Devices (IEDs)(临时组装的爆炸装置）thatcan be assembled from materials not dangerous by themselves. “So we’re now asking dogs notjust tofind a needlein a haystack (干草堆）一 now the problem is more like saying to the dog we need you to find any sharp object in the haystack,” says Clive Wynne, a professor atArizona State University.
Wynne directs the study that develops methods to train dogs to identify a wide variety of ingredients that could be used to make bombs. The dogs not only have to detect whether explosive materials are present, they also have to determine if the chemicals they smell could combine to form an explosive mixture. The dogs need to learn that when combined with other elements, even sugar could be used in a bomb. “we want the dogs to grasp the concept of ‘this might explode’”
Wynne says the big problem is that IEDs are just that---improvised and completely unsteady. A dog’s nose can be over a thousand times more powerful than a human’s nose. Some agencies spent billions of dollars over the last 15 years trying to create a technical replacement for the nose of the dog, and at the end of all that they just had to admit “No, we cannot get close”Wynne thinks his team candevelop bomb sniffing (嗅，闻）dogs that can detect IEDs at a small part of that price. All it takes is patience.
According to the passage， the new task of bomb-detecting dogs is to learn_______ .
本题考查推理推断题。根据第一段中的第一句最后的“a new challenge： Bomb-detecting dogs now have to learn to find the increasingly common Improvised Explosive Devices(IEDs)(临时组装的爆炸装置）that can be assembled from materials not dangerous by themselves.” 可以得知，炸弹侦探犬的新的挑战是侦探出可以用来制造炸弹的材料。故答案A是正确选项。
The word “ingredients” (Line 2, Para. 2) is closest in meaning to________.
本题考查猜词题。根据第二段第一句“Wynne directs the study that develops methods to train dogs to identify a wide variety of ingredients that could be used to make bombs” 可以得知ingredients是用来制作炸弹的，制作炸弹得需要各种成分，故答案D是正确选项。
According to the passage， a dog’s nose________?
本题考查推理推断题。根据最后一段的“Some agencies spent billions of dollars over the last 15 years trying to create a technical replacement for the nose of the dog, and at the end of all that they just had to admit “No, we cannot get close”.” 可以得知，一些机构花巨资研发代替够鼻子的东西，但是最后不得不承认没有效果。故B选项为正确答案。
Why is it difficult to train dogs to detect IEDs, according to Wynne?
本题推断题题。根据第二段第一句“Wynne directs the study that develops methods to train dogs to identify a wide variety of ingredients that could be used to make bombs”和最后一段“Wynne says the big problem is that IEDs are just that---improvised and completely unsteady”可以得知，可以得知困难之处在于IEDs可以是各种材料制作而成。故D选项为正确答案。