下列判断正确的是[ ]
A.酸酐一定是氧化物
B.分子晶体中一定存在化学键
C.碱性氧化物一定是金属氧化物
D.正四面体分子中键角一定是109°28′
答案:C
______ the temperature might drop, coal was prepared for warming.
A.To consider
B.Considered
C.Considering
D.To be considered
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