高岭土的组成可表示为Al2Si2Ox(OH)y,其中x、y的数值分别是 [ ]
A.7,2
B.5,4
C.6,3
D.3,6
答案:B
如图表示交变电流的图象是( )
A.
B.
C.
D.
If you()a magnet-needle, its two ends can point North and South, and so it can be used to determine directions.
A.overtake
B.fix
C.highlight
D.suspend