European football is played in about 80 countries, ____ (make) it the most popular sport in the world.
生殖和幼体发育必须在水中进行,幼体要经过变态发育才能进行陆上生活的动物类群是( )
若|x﹣ 12 |+(y+2)2=0,则(xy)2015的值为( )