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问题 填空题

已知一个三角形的两边长分别是3cm 和4cm ，则第三边长x 的取值范围是（    ）。

若x是奇数，则x的值是（    ）；这样的三角形有（    ）个；

若x是偶数，则x的值是（    ）；这样的三角形又有（    ）个。

答案

1cm<x<7cm；3cm，5cm；2；2cm，4cm，6cm；3。

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.\

8（）

A.popular

B.common

C.ordinary

D.widespread
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单项选择题

当纤芯需要查找时，需要的仪表是（）。

A、光源和光功率计

B、仅仅用OTDR

C、万用表
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