A:①②
B:③④
C:②③
D:①④
Hello,I'm Fangfang. I'm 10. My favourite letter is A. Yellow is my favourite colour. This is Sam. The ABC song is his favourite song. His favourite colour is blue. D is his favourite letter.
①钠的化合物②能与硝酸反应的物质 ③可溶于水的物质 ④水溶液导电 ⑤钠盐 ⑥钠的含氧化合物.
下图反映的是新中国在20世纪五六十年代的农业经济发展状况,出现图中B点到C点这一变化的主要原因是( )