题干

对实验过程的评价,正确的是(  )


A:向某无色溶液中滴入石蕊试液,石蕊试液变蓝色,则该溶液是碱溶液

B:某溶液滴加BaCl2试液,生成不溶于稀硝酸的白色沉淀,则该溶液中一定含有SO42﹣

C:某溶液滴加稀HCl,无现象,再滴加BaCl2试液生成白色沉淀,则该溶液含有SO42﹣

D:某钠盐溶液加入稀盐酸后会产生CO2气体,则该溶液是Na2CO3溶液

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答案(点此获取答案解析)

C

同类题1

阅读理解

A report by UNEP联合国环境规划署(United Nations Environment Programme) says that by 2050, the world's population is expected to reach 9.6 billion and feeding us all will require at least 60% more food than we have ever produced before. What's more, if we can't find out a way to do with it, food shortages (短缺) could be a big problem.

A main purpose of the report is to make people be aware of the importance of this challenge. In the past, food production increase relied on the practices like cutting down trees, using chemicals and wasting water. Today we understand the environmental price of those techniques.

“The question now is how to produce much more food and at the same time avoid all the environmental problems that we had in the past,” Searchinger, a famous scientist said.

We need to develop new ways to produce food. We can no longer cut down trees. Instead, we'll have to protect water and land, and reduce air pollution.

The report also mentions the importance of reducing food loss and wasteAccording to the United Nations, the waste adds up to one-third of all the food we produce —an amount that could feed an additional 2 billion people.

The report also suggests that we make changes in our diet. “You have to eat more efficiently (有 效地),” said Searchinger, “and above all that means eating less meat, and especially reducing the growth of beef.”That's because raising cows is an inefficient way of producing food. Of all the energy that goes onto feeding cows, only about 1% is converted (转换) into food for people.

同类题3

阅读《瘦马铜声》,完成下面问题。
                                                                                                             瘦马铜声①
                                                                                                              张守印
         ①马霜天马老师夹着课本,微笑着走进教室时,顽劣的初二(2)班的小男生小女生差点没笑出声来:一米八的瘦削身架,鼻梁上架着副很夸张的眼镜,以至于半个面孔都闪烁在厚重的玻璃镜片的后面,给人以一种头重脚轻的感觉。
         ②虽然早有“探马”来报,这个从外校新调来的班主任,是专带差班的高手,很有能耐,但他是我们的对手吗?要知道,这个班一年中气走了三个班主任。
        ③第一节课,水波不兴,45分钟在马老师的微笑和同学们的游离目光中平静度过。马老师走出教室。走出教室的马老师身后被一双双明亮的眼睛盯着。他们在证实一则听到的消息:马老师的右腿有点跛。是的,上大学时马老师在一次篮球赛中,摔折了腿。医生的轻率治疗,使他的右腿短了那么一点点。走快的时候,便有了跌宕起伏的效果。此时的马老师并不知道他行走的姿势已经令他的学生产生了小小的兴奋。
        ④下午自习课。马老师走进教室时,便见黑板前围着一群同学,见他来,便轰地四下散开。黑板上画着一幅画:一匹嶙峋的瘦马直立着后腿,马脸上很滑稽地罩着副大大的眼镜。旁边有诗两句:“远看金鸡独立,近看瘦马悬蹄。”马老师看看画,又看看全班同学。此刻,全班每个人都努力呈现出“与己无关”的坦然神情,但又不时地瞟着老师的面部表情。马老师笑笑,在诗的后面挥毫续上:“行走风吹落叶,躺下长短不齐。”问:“此意如何?”全班同学一下子如绷断的弦、决堤的水,大笑不已。
         ⑤马老师不笑,作严肃状:“今后这位同学可任语文科代表,兼出黑板报。”全班复大笑,可笑着笑着,都不笑了。诗画作者吴晓阳慢慢站了起来,红着脸,嘴唇翕动着想说什么。马老师微笑着拍拍他,示意坐下。复转身,在黑板上重重写下四个字:尊师重教。
          ⑥于是,每日踏着晨光,路上、校园里,处处都能听到初二(2)班同学嘹亮的声音。马老师的自豪溢于言表:到处都是我们班的人。有的同学低头走路,马老师会很认真地走到他面前,喊一声:同学好!在你小吃一惊之后,你会看到一个高出你一个多头的瘦长个子和他从镜片后荡漾出的微笑。半月后,师生互致问候蔚然成风。
        ⑦马老师教数学。热门的主科教师大抵都做家教,可马老师不做家教。不做家教的马老师便成了“另类”。老婆劝他挣一份家教钱,补贴家用。马老师说,手心手背都是身上的肉,好生差生都是我的学生。于是,便自己给自己加课,弄得累累的。后来,拗不过几个差生家长的苦苦恳求,开了小灶,可又不收人家的钱。有人便说,鲁迅笔下的孔乙己还晓得没钱先赊碗黄酒,他怎么这么迂?
        ⑧马霜天的班主任固若金汤,一连当了两年。这个班的成绩扶摇直上,从全年级最后一名,一口气超过5个班,直逼第一名。
        ⑨初三毕业前的最后一次班会,马老师照例微笑着走进教室,吴晓阳早已又在黑板上画了匹瘦马,马脸上还是罩着副大大的眼镜,旁边写了四个字:“瘦马铜声”。见老师进来,班长走上讲台,用红粉笔写下了一横。马老师惊诧,怎么不写了?只见全班45位同学按学号,一个接一个上来,每人也只写了一笔。黑板上出现了醒目而鲜红的六个大字:“老师,我们爱您!”
        ⑩掌声响起来,持久而热烈。马霜天老师的眼睛湿润了,有晶亮的东西要涌出来。
                                                                                                                                                 (有删改)
        [注]①“瘦马铜声” 一词出自唐代诗人李贺的咏马诗。“铜声”意为铜声悦耳,表明器质精良。这一词语生动地显示了这匹马骨力坚劲的美好素质。诗人借天马来讴歌逆境中人的高尚品德与气节。