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【单选题】
将E-R图向关系模型的转换中,如果两实体之间是一对多(1:n)的联系,所转换的关系模型的主键由( )担任。A.
双方实体的主键联合
B.
1端实体的主键
C.
任一方实体的主键
D.
n端实体的主键
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【单选题】Noxious emissions amount to 0.25~0.4 percent by volume of the___ ,depending on the amount of sulphur in the fuel and its lower heat value, and the engine type, speed and eficiency Noxious emissions有毒排...
A.
sulphur
B.
suction air
C.
exhaust gas
D.
discharging air
【简答题】Many nations are restricting emissions of noxious gases. The noxious gases threaten the atmosphere.
【简答题】Identify from which paragraph the information is derived. China is adopting European standards in controlling the emissions of noxious car exhausts.
【判断题】标定I2溶液时,既可以用Na2S2O3滴定I2溶液,也可以用I2滴定Na2S2O3溶液,且都采用淀粉指示剂。这两种情况下淀粉指示剂的时间是相同的。( )
A.
正确
B.
错误
【单选题】By ( ), besides burning coal, other noxious emissions from industry and vehicles were added to the mix of London’s air pollution.
A.
The mid-19th century
B.
The mid-20th century
C.
The end of 19th century
D.
The beginning of 21st century
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