题干

某校生物兴趣小组,为了探究某些生态因素在生态系统中的作用,用四个相同鱼缸设计了如下实验,分析并回答下列问题.

环境因素

A缸

B缸

C缸

D缸

清水/mL

1000毫升

1000毫升

1000毫升

1000毫升

河泥/g

100克

100克

等量水藻

状态相同小鱼/条

5条

5条

5条

5条

光照

适宜光照

适宜光照

适宜光照

黑暗

小鱼生存时间/天

3天

11天

25天

2天

(1)如果要研究光照在生态系统中的作用,应选取哪两组实验装置____ ,如果要研究水藻在生态系统中的作用,应选取哪两组实验装置? ____ 

(2)如果选择A和C两组实验装置作为对照实验,能否说明河泥在这个生态系统的作用?____ 说说理由.____ 

(3)如果将B和C两组实验作为对照实验,请你提出一个与此相关的探究问题:____ 

上一题 下一题 0.0难度 选择题 更新时间:2017-04-03 11:36:10

答案(点此获取答案解析)

C和D,A和B,不能,因为A、C两个装置中有河泥和水藻两个变量,河泥对小鱼生存时间有影响吗?

同类题3

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,并在答题卡上将该项涂黑。选项中有两项为多余选项。

                                                                       Wrong Reasons for Going to College

    A college education can be priceless.____If any of these following factors had abig influence on your decision, you're probably right to second-guess yourself.

   Because all your friends are going.

    In only a few weeks' time, the whole friend group will be scattered to a half dozen different colleges in a half dozen different places. Not to go will set yourself apart.____Because someone else expects it from you.

    Perhaps you come from a family where everyone goes to college,or maybe you're the kid that everyone is proud to believe will be the first toget there.____It's become so mucha part of the air you breathe that you've never stopped to consider whether you want to go or whether you're ready to go.

    ____It's beentough to find even a summer job. You don't have an alternative plan. Everyone else is doing it (see above). You think you might as well go to school. That isthe lamest(无说服力的)of reasons tospend $ 20,000 or more in the next year.

    Because you are afraid you'll regret it if you don't go.

    Your uncle tells you that he regrets that he didn't go tocollege. Others tell you they could have gone so much further in their career if only they had a college education.  ____ So this is not a persuasive reason for you togo to college.

a. A. Because you don't want to work.

b. Friends will wonder what's wrong with you.

c. Because you don't know what else to do.

d. Everyone seems more excited than you are.

e. It seems that for years everyone has just thought that ofcourse you'll go.

f. Whatever the story is, there are always people who regretdecisions they've made.

g. But maybe in your heart you know that you are going forthe wrong reasons.

同类题4

阅读下文,回答相关问题

                                                                                                   我的麦子熟了
        14岁的高占喜,青海农家子弟,因为湖南卫视的《变形计》,他和城市的一个叫魏程的富家少年互换了7天人生。节目打出了议题:7天之后,高占喜愿意回到农村吗?
        第一天,占喜在机场被新爸新妈接进了豪华的宝马车,他害羞地靠在真皮座椅上面,不说话,认真地看着窗外闪过的高楼大厦,忽然,他泪水盈眶。
这个以前在山沟里疯跑,活泼开朗的孩子,曾经在作文里写道:我想考上大学,在城里生活。可是他知道,他更可能中途辍学,流浪在城市某条喧嚣的马路上。这次机缘巧合,他提前进入了城市,小小的心里波澜起伏,何况现实的城市,比那个瑰丽的梦,仿佛更精彩。
        占喜住进了一栋豪华如天堂的复式公寓,拥有一间无比舒适的大卧室。面对丰盛的晚餐,他无所适从,紧张得5次掉筷子。接着,新爸新妈一次给了他200元的零花钱。从前,他一个月只有1元的零花钱。
         在气派的理发店里,占喜看到镜子里的自己,又一次泪水盈眶。
         不久,他迅速适应了这种新生活。
         白天,他靠在松软宽大的沙发上,茶几上是他之前从未见过的零食,面前是尺寸巨大的液晶电视。他自在地享受这一切,除了脸颊上两抹褪不去的高原红,就像是在这里长大的。
         此时,观众们忧心忡忡——这个孩子会丧失本性,沉迷于吃喝玩乐吗?
         某天,占喜被安排去卖报。归途中,占喜变得少言寡语。他看到城里人行色匆匆,在马路之间穿梭,犹如他在田间穿梭,也看见天桥下的乞丐,衣衫褴褛地等待施舍……那天,他对记者说,城里人也有穷人,生活也不容易。记者问,那你同情他们吗?占喜说,不,每个人都有一双手,幸福靠自己。
说话时,他分明又是那个崇尚奋斗、一直努力的高原孩子。
         当晚短信预测,大多数观众仍然觉得占喜不愿回乡。然而,谜底提前揭晓——当占喜得知父亲不慎扭伤脚的消息时,他立刻要求赶回家乡。
       “为什么急着要走?父亲的脚伤不是大事,难得来一次城里。”记者问。
         占喜只说了一句:我的麦子熟了。
         父亲很早双眼失明,哥哥在外打工,弟弟还年幼,14岁的占喜已经成为家里的主要劳力。他难以不被城市吸引,这无可厚非,但同时,他也眷恋自己贫穷的家、艰辛的父母、几亩薄田和已经成熟的麦子。
         城市是他的梦,贫穷的家,却是他牵肠挂肚的现实世界。
         回到农村后,占喜仍然五点半钟去上学,啃小半个馍馍当午餐,学习之余割麦挑水,补丁长裤配布鞋,刻苦读书不改初衷:只有不断学习,才能真正走出大山,改变命运。
        占喜见识了前所未见的繁华都市,享用过从未经历的物质生活,却始终未曾忘记自己是个印着高原红的孩子,未曾忘记担当家的责任——“我的麦子熟了”,当《浮士德》的俗世诱惑变相重演,这是一句最朴实的箴言。