由于瓦斯具有()的特性,所以可将瓦斯作为民用燃料。
A.可燃烧
B.无毒
C.无色、无味
D.窒息
参考答案:A
Where were you at supper time? I _____ for you to join me. [ ]
A. waited
B. had waited
C. have been waiting
D. was waiting
丁二酮重量法测定钢中镍,在pH8~9的氨性溶液中进行,原因是()
A、便于共沉离子Fe3+,Cr3+等一起沉淀
B、丁二酮胿是二元有机弱酸
C、减小丁二酮的酸效应
D、酒石酸在较高Ph下的掩蔽效果好