釉质发育不完全的患牙比正常牙的釉质,X线片上显示牙冠部密度减低,牙冠磨耗变短小。()
A.增厚
B.密度增加
C.减低
D.薄
参考答案:D
At the shopping centre, she didn’t know what _____ and ______ with an empty bag.
A.to buy, left
B.to buy, leave
C.to be bought, left
D.was to buy, leave
写出下列物质的化学式:
(1)五氧化二磷______;
(2)高锰酸钾______;
(3)水______.