若x，y为实数，且|x+2|+$\sqrt{y-2}$=0，则（$\frac{x}{y}$）²⁰¹⁵的值为（　　）

下列各项中，属于细胞分化、癌变和衰老共同特征的是(　　)

B

    Researchers say they have created a new super-tough material in the laboratory. It is stronger, lighter and costs less than steel. But the new material is not a product of high technology. It is wood. Researcher Liangbing Hu says that it can compete with some of the world's strongest materials or even replace steel.

    The product is called Super Wood. It doesn't require any special raw, unprocessed material. That means the cost of the product will be relatively low.Hu said, “We can start with very cheap wood, and also very fancy, expensive wood. But in the end, we get very similar performance.”

    Super Wood is made by partially removing a natural polymer called lignin（木质素）. Hu explained, “Lignin is like glue to hold all the parts together in natural wood. To be able to densify（增密）the wood completely, some of the lignin has to be removed. “Strong chemicals are put on the wood to remove about half of its lignin. Then, after being left in extreme heat and pressurized for a day, the treated wood is ready.

    The wood is strong enough to build automobiles, airplanes, wind turbines and more. Researchers are finding many new ways to use wood, including creating batteries and see-through wood and paper.Hu said, “Wood has been existing on Earth for more than a million years. And human beings have been using wood for furniture, construction for more than 10 thousand years. And the more we worked on this material, we realized, we have never fully exhausted the potential of this amazing material.”