题干

土壤板结不利于植物生长,其直接原因是(  )

A:缺少肥力,减弱光合作用

B:缺少水分,减弱光合作用

C:缺少二氧化碳,减弱根的呼吸作用

D:缺少氧,减弱根的呼吸作用

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答案(点此获取答案解析)

D

同类题4

阅读理解

    “Years ago when I was at the Grand Canyon, I remembered someone coming up to the canyon's edge, taking a shot with a camera and then walking away, like 'got it – done', barely even glancing at the magnificent scene in front of him,” Linda Henkel, a scientist at Fairfield University, US told Live Science.

    Henkel was surprised by how obsessed (痴迷的) people are with taking pictures these days - before dinner, during friends' birthday parties, on museum tours and so on.

    They keep taking pictures because they think that it helps record the moment, but as Henkel's latest study has just found out, this obsession may prevent their brains remembering what actually happened, reported The Guardian.

    In her study, Henkel led a group of college students around a museum and asked them to simply observe 15 objects and photograph 15 others. The next day the students' memory of the tour was tested, and the results showed that they were less accurate in recognizing the objects and they remembered fewer details about them if they photographed them.

    ''When people rely on technology to remember them — counting on the camera to record the event and thus not needing to attend to it fully themselves, it can have a negative impact on how well they remember their experiences,” Henkel explained.

    But there is also an exception: if students zoomed in to photograph part of an object, their memory actually improved, and those who focused the lens (镜头) on a specific area could even recall parts that weren't in the frame.

    So basically, this study is saying that constantly taking pictures can harm your memory. But shouldn't reviewing pictures we have taken help wake up our memories? This is true, but only if we spend enough time doing it.

    “In order to remember, we have to access and interact with the photos, rather than just collect them,” Henkel told The Telegraph. However, previous research has shown that most people never take the time to look over their digital pictures simply because there are too many of them and they aren't usually very organized on their computers.

同类题5

阅读材料,完成下列要求。

材料一:1798年,英国的人口理论学家马尔萨斯在《人口论》一书中指出:人口在无所妨碍时,以几何级数率增加,即以1,2,4,8,16,32,64的增加率增加;食物将以1,2,3,4,5的算术级数增加率增加。因人口增长速度快于食物供应的增长速度,人口将超过食物的供给量,而食物不足会引起贫困、恶习等出现。人口与食物间的不平衡总是通过抑制人口增长而加以改善。他提出两类抑制人口增长的方法为:道德抑制与积极抑制。他主张人们应通过晚婚、独身、节育来控制出生率;但若人们未能通过道德控制住人口的增长,则恶习、贫困、战争、疾病、瘟疫、洪水等各种形式的积极抑制将会使人口减少,以达到人口增长与食物供应间的平衡。马尔萨斯反对社会改革论,认为社会中的贫穷和罪恶并不是社会经济和政治制度造成的,而是人口规律作用的结果,只有保持财产私有制以及各人担负起养育自己孩子的责任,才能使人们自制,不至于生殖过多的子女。他竭力反对当时英国实行的济贫法,济贫法使不能独立维持家庭的人也将结婚,生育子女,这是供养贫民以创造贫民。马克思指出马尔萨斯的《人口论》所以轰动一时,完全是由于党派利益引起的。英国的寡头政府认为它可以最有效的扑灭一切追求人类进步的热情,因而报以热情的喝彩。

——摘编自《马尔萨斯人口理论的评价与中国人口问题》

材料二:孙中山1924年在广州国立高等师范学校所作的演讲中指出:“中国人时常自夸,说我们人口多,不容易被人消灭……殊不知百年之后,美国人口可加到十万万,多过我们人口两倍半。如果美国来征服中国,那么百年之后,十个美国人中只参杂四个中国人,中国人便要被美国人所同化。……百年前有一个英国学者,叫做马尔赛(萨)斯,他因为忧世界上的人口太多,供给的物产有限,主张减少人口。中国现在的新青年,也有被马尔赛(萨)斯学说所染。”孙中山的这种人口思想的影响极为深远。

—摘编自《孙中山人口思想研究》等