某浓溶液的溶质质量分数为m%，稀溶液的溶质质量分数为n%，混合后_爱下问搜题

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问题选择题

某浓溶液的溶质质量分数为m%，稀溶液的溶质质量分数为n%，混合后溶液的溶质质量分数为A%，则混合前，浓溶液与稀溶液的质量比是（　　）

A．m：n

B．（A-n）/（m-A）

C．（m+n）/200

D．（A-n）/（a+m）

答案

设浓溶液的质量为x，稀溶液的质量是y．

根据质量分数=

溶质的质量

溶液的质量

×100%，得

溶质的质量=质量分数×溶液的质量，

所以，浓溶液的溶质的质量=xm%，

稀溶液的溶质的质量=yn%，

则A%=

xm%+yn%

x+y

×100%，则

x

y

=

A-n

m-A

；

故选B．

单项选择题

管理的环境可分为( )和具体环境两大类。

A．一般环境

B．政治环境

C．社会环境

D．经济环境

完形填空

I used to be a very self-centered person, but in the past two years I have really changed. I have started to think about other people        I think about myself. I am happy that I am becoming a       person.
I think my        started when I was at Palomar College. At first, I just wanted to get my       and be left alone. I thought I was smarter than everyone else, so I hardly ever         to anyone in my classes. By the end of my first semester, I was really        . It seemed as if everyone but me had made friends and was having fun. So tried a (n)        . I started asking people around me how they were doing, and if they were having trouble I       to help. That was really a big        for me. By the end of the year, I had several new friends, and two of        are still my best friends today.
A bigger cause of my new        , however, came when I took a part-time job at a Vista Nursing Home. One old lady there who had Alzheimer’s disease became my         . Every time I came into her room, she was so       because she thought I was her daughter. Her real daughter never        her, so I took her place. She let me       that making others feel good make me feel good, too, when she died, I was       , but I was very grateful to her.
I think I am a much        person today than I used to be, and I hope I will not        these experiences. They have         me to care about other people more than about myself. I        who I am today, and I could not say that a few years ago.

B．heartbroken

C．bad-tempered