中国古代小农生产最基本的耕作方式是
A.刀耕火种
B.铁犁牛耕
C.石器锄耕
D.个体经营
答案:B
“复盐”是指由多种简单阳离子和一种酸根离子组成的盐,如KAl(SO4)2;而由一种金属离子与多种酸根离子构成的盐则称为“混盐”,如氯化硝酸钙[Ca(NO3)Cl]。下列化合物属于混盐的是 [ ]
A. CaOCl2
B. (NH4)2Fe(SO4)2
C. BiONO3
D. K3[Fe(CN)6]
If we _______ adequate preparations, the conference wouldn't have been so successful.[ ]
A. haven't made
B. wouldn't make
C. didn't make
D. hadn't made