题目

Our home galaxy(星系), the Milky Way, makes for a pretty space picture, and it looks normal at a distance. But a new 3D map reveals a surprise:_______________________________.The Milky Way is a spiral(漩涡型的) galaxy, in which stars and gas clouds exist mainly in its spiral “arms”. Our massive neighbor, the Andromeda galaxy(仙女座), is also spiral. Spiral galaxies usually appear very flat and easy to see through a telescope, said the researchers.Using 1,339 large, pulsating(脉冲的) stars to make a 3D map of the Milky Way, researchers discovered instead that the galaxy’s disk11．下列各式计算正确的是（　　）A．a2•a3=a6B．（-a3）2=a6C．（2ab）4=8a4b4D．2a2-3a2=1