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水中碱度和硬度有怎样的关系？

答案

参考答案：

对天然水而言，碱度和硬度之间有三种关系（1）总碱<总硬即水中「HCO3-」<「Ca2+」+「Mg2+」此时水中有永硬无钠盐碱度则总碱=暂硬即永硬=总硬—总碱（2）总碱=总硬：即水中无永硬也无钠盐碱度则总碱=总硬=暂硬（3）总碱>总硬：水中无永硬有钠盐碱度则总硬=暂硬即总碱度—总硬度=钠盐碱度

阅读理解
根据表格，选择正确答案。
1988至1990年， 一个名为“人口危机委员会”的组织对世界上100个大城市进行了调查。请根据下面
12个主要大城市的调查表回答问题。
Population
(million)
(%) of
income
spent
on food
Persons
per
room
(%) if
houses with
water and
electricity
Telephones
per 100
people
(%) of
children
in high
school
Tokyo    
      28.7       
   18     
0.9 
       100        
     44     
97
Mexico City
19.4
41
1.9
94
6
62
New York
17.4
16
0.5
99
56
95
Sao Paulo
17.2
50
0.8
100
16
67
Osaka
16.8
18
0.6
98
42
97
Seoul
15.8
34
2.0
100
22
90
Moscow
13.2
33
1.3
100
39
100
Bombay
12.9
57
4.2
85
5
49
Calcutta
12.8
60
3.0
57
2
49
Buenos Aires
12.4
40
1.3
86
14
51
 Los Angeles
11.5
12
0.5
94
35
90
London
11.0
24
0.6
100
50
58
1. Of the following cities, people live in ____ spend least of their income on food.
[ ]
A. Mexico City
B. Buenos Aires
C. Calcutta
D. Bombay
2. Which city has the most people?
[ ]
A. New York.
B. Moscow.
C. Tokyo.
D. London.
3. The number of the students studying in high schools in Tokyo out of 100 students is the same as that of
    _____.
[ ]
A. Seoul
B. Sao Paulo
C. Calcutta
D. Osaka
4. In which city do all the houses have water and electricity?
[ ]
A. London.
B. Los Angeles.
C. New York.
D. Bombay.
5. It is the most difficult for people in _____ to make a phone call.
[ ]
A. Sao Paulo
B. Mexico City
C. Bombay
D. Calcutta
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问答题 简答题

简述生物多样性三个层次。
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