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【单选题】
命题“若 =0,则 =0或 =0”的逆否命题是A.
若 =0或 =0,则 =0
B.
若 ，则 或
C.
若 且 ,则
D.
若 或 ，则
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反馈参考答案：
举一反三
【单选题】测量一约为1.5伏的电压时要求其结果的相对误差不大于1.5%,则应选用下列哪种规格的电压表:
A.
0.5级,量程为5伏
B.
1.0级,量程为2伏
C.
2.5级,量程为1.5伏
D.
0.5级,量程为1.5伏
【单选题】ZPW-2000R型无绝缘轨道电路在最不利条件下，用0.15Ω标准分路线分路，主轨道无分路死区段。调谐区分路死区段不大于（）。
A.
2m
B.
3m
C.
4m
D.
5m
【单选题】ZPW-2000R型无绝缘轨道电路在最不利条件下,用0.15 Ω标准分路线分路,主轨道无分路死区段。调谐区分路死区段不大于( ):
A.
2 m
B.
5 m
C.
4 m
D.
3 m
【单选题】British banks move their headquarters to South Africa because ______.
A.
South Africa is a safer country compared with others in Africa
B.
South Africa is gradually becoming a financial center in Africa
C.
South Africa offers preferential banking terms to foreign banks
D.
South Africa is a platform. in Africa for the American investors
【单选题】English is also spoken in Singapore and Malaysia and countries in Africa _________ South Africa.
A.
for example
B.
for instance
C.
such as
D.
such like
【单选题】ZPW-2000R型无绝缘轨道电路信号机安装需要满足建筑接近限界要求，安装在调谐区距匹配单元（）的位置。
A.
大于或等于2m
B.
小于或等于2m
C.
大于或等于2.5m
D.
大于或等于2m、小于或等于2.5m
【简答题】In Africa, thereare a lot of children suffering from ______(severity) malnutrition.
【简答题】Africa has the highest birth rates in the world, and today the total population in Africa is ______.
【单选题】Africa's elephants are divided between the savannahs of eastern and southern Africa and the forests of central Africa. Some biologists reckon the forest ones-smaller, with shorter, straighter tusks-ma...
A.
Biological evidences are insufficient to support this point of view.
B.
The high price of ivory entices more killings of elephants.
C.
Their number is too small to be of a species.
D.
A serious disease broke out among the elephants and sharply decreased their number.
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