t℃时，某盐溶液120g，蒸发掉20g水或加入5g该盐后，溶液均达到饱_爱下问搜题

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问题选择题

t℃时，某盐溶液120g，蒸发掉20g水或加入5g该盐后，溶液均达到饱和，则原溶液的质量分数为（　　）

A．20%

B．4%

C．16.7%

D．20.8%

答案

该溶液蒸发20克水，加入5克溶质都会饱和，也就是说20克的水中可以溶解5克的溶质，设原溶质为x，

原溶液的溶质为：（120-20）：x=（20+5）：5

x=20，

所以溶质质量分数为：

20

120

×100%=16.7%

故选C．

阅读理解

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单项选择题 A1/A2型题

髋关节中心型脱位宜采用持续牵引治疗，时间一般是（）

A.3～4周

B.4～6周

C.6～8周

D.8～10周

E.3个月以上