题目

Recently, a solar-powered(太阳能动力的) plane took to the sky for the first time. It passed an important test on the way to travel around the world.The plane took off from an airport(飞机场) in Switzerland. It slowly rose above the fields and into the sky.“There was never a plane of that kind that could fly—never a plane so big, so light, using so little energy.” Said Bertrand Piccard, a leader of the project.During the 90-miunte flight(飞行), the plane did several turns. It climbed 1.6 km above the countryside.Engineers plan to test a night flight(飞行) before July. Then th将分式x2x+y中的x、y的值同时扩大2倍，则扩大后分式的值（　　） A、扩大4倍B、扩大2倍C、缩小2倍D、保持不变