普鲁卡因含有的中间链是()
A.碱基(RN)
B.阳离子(RNH’)
C.离解常数(pKA.
D.酯链(—CO—)
E.酰胺链(—CNH—)
参考答案:D
It puzzles the scientists _____ some mammals produce their young _____ others lay eggs.
A.that; while
B.what; while
C.that; as
D.what; as
进入油区不能穿钉子鞋是为了防止产生()。
A.火花
B.静电
C.响动
D.噪声