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【单选题】
函数y=-2x+4如果-2≤y≤2 则x的相应取值范围是 [ ]A.
-2≤x≤2
B.
-3≤x≤-1
C.
1≤x≤3
D.
-1≤x≤3
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举一反三
【单选题】用已知浓度的盐酸来测定某Na 2 CO 3 溶液的浓度时，若配制Na 2 CO 3 溶液时所用Na 2 CO 3 中分别含有： ①NaOH②NaCl③NaHCO 3 ④K 2 CO 3 杂质，所测结果偏低的是 [ ]
A.
仅①
B.
仅②
C.
仅②③
D.
②③④
【单选题】In what way armed robberies are Americanized in Britain?
A.
Handguns instead of shotguns are used in armed robberies.
B.
Convenience stores become the targets at night and the criminals are not professional.
C.
British police find it is very difficult to crack the crime as American police.
D.
There is a sharp rise of robberies committed by Americans in Britain.
【简答题】The whole country was armed in a few days.英译汉
【单选题】配制 C ( Na 2 CO 3 )= 0.5mol • L -1 溶液 500ml ,应称取 Na 2 CO 3 ( )g 。 M ( Na 2 CO 3 )= 106 g . mol -1 。
A.
20
B.
25
C.
26.5
D.
30
【单选题】配制以下标准溶液必须用间接法配制的是 ( ) NaCl Na 2 C 2 O 4 NaOH Na 2 CO 3
A.
NaCl
B.
Na2C2O4
C.
NaOH
D.
Na2CO3
【单选题】配制Na2CO3 溶液(0.01mol/L)100ml,已知Na2CO3 分子式 105.99,称取Na2CO3()
A.
0.1060g
B.
0.1820g
C.
0.1925g
D.
0.2030g
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