搜题请搜索小程序“爱下问搜题”
问题 选择题

北京是中 * * 、全国人大常委会和国务院所在地，全国政协、最高人民法院、最高人民检察院也在北京，国务院各部委、各人民团体的中央机构都在北京办公，与我国建立外交关系的各个国家都在北京设立了驻华使馆。以上这些都说明了北京的哪项城市职能[ ]

A．全国的政治中心  

B．全国的经济中心  

C．全国的文化中心  

D．全国的交通中心

答案

答案：A

选择题

在图1所示的四个情景中，属于光的直线传播形成的是

      

丹顶鹤在水中的倒影 射灯射出的光柱 铅笔在水面处“折断” 雨后的彩虹

A                B                 C                  D
查看答案
单项选择题

Most plants can make their own food from sunlight, (1) some have discovered that stealing is an easier way to live. Thousands of plant species get by (2) photosynthesizing, and over 400 of these species seem to live by pilfering sugars from an underground (3) of fungi(真菌). But in (4) a handful of these plants has this modus operandi been traced to a relatively obscure fungus. To find out how (5) are (6) , mycologist Martin Bidartondo of the University of California at Berkeley and his team looked in their roots. What they found were (7) of a common type of fungus, so (8) that it is found in nearly 70 percent of all plants. The presence of this common fungus in these plants not only (9) at how they survive, says Bidartondo, but also suggests that many ordinary plants might prosper from a little looting, too.

Plants have (10) relations to get what they need to survive. Normal, (11) plants can make their own carbohydrates through photosynthesis, but they still need minerals. Most plants have (12) a symbiotic relationship with a (13) network of what are called my corrhizal fungi, which lies beneath the forest (14) . The fungi help green plants absorb minerals through their roots, and (15) , the plants normally (16) the fungi with sugars, or carbon with a number of plants sharing the same fungal web, it was perhaps (17) that a few cheaters—dubbed epiparasites—would evolve to beat the system. (18) , these plants reversed the flow of carbon, (19) it into their roots from the fungi (20) releasing it as "payment.\

20（）

A. instead of

B. in spite of

C. in place of

D. by contrast of
查看答案