问题 问答题 简答题

水的化学性状评价指标有哪些?

答案

参考答案:PH;硬度;氮化物;氯化物;硫酸盐;溶解氧(DO);生化需氧量(BOD);化学需氧量(COD);总需氧量(TOD);总有机碳(TOC)
PH决定于它所含氢离子及氢氧离子的多少。硬度是指溶于水中的钙、镁等盐类的总含量,铁及其他矿物质有时也占一小部分。氮化物包括有机氮、蛋白质、氨氮。亚硝酸盐氮。有机氮是指有机含氮化合物的总称。蛋白氮是指已经分解成较为简单的有机氮。氯化物自然界的水一般含有氯化物。硫酸盐天然水中均含有硫酸盐,且多以硫酸镁的形态存在。溶解氧(DO)指溶解在水中的含氧量,其含氧与空气的氧分压、水温有关。BOD(生化需氧量):水中有机物被需氧性细菌作用所消耗的溶解氧量。COD(化学需氧量):在一定条件下,以强氧化剂如高锰酸钾、重铬酸钾等氧化水中有机物所消耗的氧量。可作为水中有机物含量的一间接指标。总需氧量(TOD):指一升水中还原物质(有机物和无机物)在一定条件下氧化时所消耗的氧的毫升数。总有机碳(TOC):指水中全部有机物的含碳量,它只能相对表示水中有机物的含量。

完形填空

A newly trained teacher named Mary went to teach at a Navajo Indian reservation. Every day, she would ask five of the young Navajo students to __1__ the chalkboard and complete a simple math problem from   2  homework.

They would stand there, silently,  3  to complete the task. Mary couldn’t figure it out.   4  she had studied in her educational curriculum helped, and she   5  hadn’t seen anything like it in her student-teaching days back in Phoenix.

What am I doing wrong? Could I have chosen five students who can’t do the  6 ? Mary would wonder. No,  7  couldn’t be that. Finally she   8  the students what was wrong. And in their answers, she learned a   9  lesson from her young   10  pupils about self-image and a(n)   11  of self-worth.

It seemed that the students  12  each other’s individuality and knew that  13  of them were capable of doing the problems.   14  at their early age, they understood the senselessness of the win-lose approach in the classroom. They believed no one would  15  if any students were shown up or embarrassed at the  16 . So they   17  to compete with each other in public.

Once she understood, Mary changed the system   18  she could check each child’s math problem individually, but not at any child’s expense  19 his classmates. They all wanted to learn,  20  not at someone else’s expense.

1.  A. go to                     B. come to               C. get close to             D. bring

2.  A. his                        B. their                   C. his own                  D. her

3.  A. happy                    B. willingly             C. readily                   D. unwilling

4.  A. Anything               B. Nothing              C. Everything             D. Neither

5.  A. almost                   B. certainly              C. hardly                   D. never

6.  A. question                 B. chalkboard          C. problem                 D. homework

7.  A. they                      B. it                        C. everything              D. each

8.  A. asked                     B. questioned           C. told                       D. understood

9.  A. outstanding            B. surprising            C. annoying                D. frightening

10. A. sunburned               B. tender                 C. Indian                    D. naughty

11. A. sense                      B. image                 C. way                       D. aspect

12. A. had                        B. ignored               C. respected                D. cared

13. A. none                      B. no one                C. each                       D. not all

14. A. Especially               B. Even though        C. Even so                  D. Even

15. A. lose                        B. win                     C. achieve                  D. answer

16. A. time                       B. situation              C. chalkboard             D. condition

17. A. refused                   B. rejected               C. tried                      D. promised

18. A. if                        B. so that                 C. unless                    D. in case

19. A. in favour of           B. of                       C. by means of            D. in front of

20. A. and                        B. but                     C. so                          D. or

单项选择题