Perfumers pay big money for ambergris because it is a fixative, which means it holds a smell in place on a person's body.

　　揅heap perlfumes smell good in the first hour or so and then everything is gone，” explains Bohlmann.“But expensive perfumes are much more stable.Their smell lasts much longer, for hours or even a day after you apply them.”

　　The new chemical, made from the tree genes, can be used as a fixative, too.And using yeast to make it is far cheaper than acquiring ambergris.

　　Bohlmann admits he never thought he'd get into the perfume business.But now, he says, producers have been calling to find out how to use his technology in new perfumes.

　　解题导语：制作香水需要从鲸鱼里提取龙涎香生物学家约尔格·博尔曼最近发现枞树里有一种物质可以代替龙涎香。________．ery expensive

　　解析：推理判断题。根据第二段“perfume­makers often use an ingredient that comes from sperm whales, 可知来自抹香鲸的龙涎香应该很贵故选D。________．A．being difficult to hold

　　B．having a hidden problem

　　C．needing further testing

　　D．being too similar

　　解析：词义猜测题。根据下文“There's a problem that many people wouldn't consider.”可知有一个不为人知的问题即隐藏的问题故选B。lls often used in genetic research?

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