超导材料为具有零电阻及反磁性的物质,以Y2O3、BaCO3和CuO为原料经研磨烧结可合成一种高温超导物质Y2Ba4Cu6Ox,假设研磨过程中各元素的化合价无变化,则x的值为( )
A:12
B:26
C:15
D:13
You never feel worried before an exam, how can you? Well, I've been working hard all the time. Surely I am _________ any exam.
-5÷(-5)-(-7)=( )
一Sara.Let's go to the playground to watch the basketball game!
一Good idea! I wonder which group will win.
下列省份中跨干湿地区最多的是( )。