阅读理解。

     Mrs Green lives in a small village. Her husband is dead. But she has a son. He is twenty-one and his

name is Jack. He gets work in a town and lives there. Its name is Greensea. It is quite a long way from

his mother's village, and she is not happy about this, but Jack says, "There isn't any good work for me in

the village, mother, and I can get a lot of money in Greensea and give you some every week" One day

Mrs Green is very angry. She gets on a train and goes to her son's house in Greensea. Then she says to

him, "Jack, why do you never give me a ring?" Jack laughs and says, "But, mother, you don't have a

telephone." "No", she says, "I don't have one, but you have one."

1. Mrs Green lives _____.

A. in a big city

B. in a small village

C. in a town with his son

2. Mrs Green's son is

A. twelve    

B. twenty    

C. twenty-one

3. Please find a wrong sentence. _____.

A. Greensea is the name of a factory

B. Jack works in a town and his mother is unhappy about this

C. In the village there is no good work for Jack

4. The woman goes to Greensea ____ one day.

A. on a bike    

B. on foot   

C. by train

5. That Jack never telephones his mother is because _____.

A. he is too busy

B. he lives far from his mother's village

C. she doesn't have a telephone

某硫酸工厂的酸性废水中砷（As）元素含量极高，为控制砷的排放，采用化学沉降法处理含砷废水，工艺流程如下：

相关数据如下表，请回答以下问题：

表1．几种盐的K_sp

表2．工厂污染物排放浓度及允许排放标准

（1）该硫酸工厂排放的废水中硫酸的物质的量浓度c(H₂SO₄)=           mol·L^－1。

（2）若酸性废水中Fe³⁺的浓度为1.0×10^－4mol·L^－1，c(AsO₄^3－)=          mol·L^－1。

（3）工厂排放出的酸性废水中的三价砷（H₃AsO₃弱酸）不易沉降，可投入MnO₂先将其氧化成五价砷（H₃AsO₄弱酸），MnO₂被还原为Mn^2＋，反应的离子方程式为                                             。

（4）在处理含砷废水时采用分段式，先向废水中投入生石灰调节pH到2，再投入生石灰将pH调节到8左右使五价砷以Ca₃(AsO₄)₂形式沉降。

①将pH调节到2时废水中有大量沉淀产生，沉淀主要成分的化学式为             ；

②Ca₃(AsO₄)₂在pH调节到8左右才开始沉淀，原因为                               

                                                                           。

③砷酸（H₃AsO₄）分步电离的平衡常数(25℃)为：K₁=5.6×10^－3 K₂=1.7×10^－7 K₃=4.0×10^－12，第三步电离的平衡常数的表达式为K₃=                           。Na₃AsO₄的第一步水解的离子方程式为：AsO₄^3－+H₂OHAsO₄^2－+OH^－，该步水解的平衡常数（25℃）为：                  （保留两位有效数字）。