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问题 填空题

如图所示，用弹簧测力计拉一木块，在水平地面上匀速前进．该弹簧测力计的量程是______N，弹簧测力计刻度盘上的每一小格表示______N，该物体受到水平向右的拉力是______N．

答案

如图所示弹簧测力计，它的最大刻度值是10N；刻度上每一小格表示0.4N；

弹簧测力计的读数是2N+3×0.4N=3.2N，则物体对测力计的拉力为3.2N，所以该物体受到水平向右的拉力是3.2N；

故答案为：10，0.4，3.2．

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.\

15（）

A.in turn

B.in fact

C.in return

D.in the end
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选择题
一个阻值为R的电阻两端加上电压U后，通过导体截面的电量q与通电时间t的图象如图所示，此图线的斜率（即tanα）等于（　　）

A．U

B．R

C．U/R

D．R/U
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