利用SmarArt图形,可以非常直观地说明（）等常见关系

设R是集合A上的二元关系，假定存在s和t，且s＜t，使R^s=R^t，则：

设A={a，b，d，e，f}，R是A上的二元关系及其关系图如图C4所示．

试用关系矩阵法求最小自然数s、t，使s＜t且R^s=R^t．

设R是集合A上的二元关系，假定存在s和t，且s＜t，使R^s=R^t，试证明：

  (1)对所有k≥0，R^s+k=R^t+k；

  (2)对所有k，i≥0，R^s+i+kp=R^s+i，其中p=t-s；

  (3)令S={(R⁰，R¹，R²，…，R^i-1}，则对所有q∈N，有R^q∈S．

  A．RT/n_iF  B．RT/F

  C．2.303×10³RT/n_iF D．2.303RT/n_iF

Arthritis c关节炎) is an illness thatcan cause pain and swelling in your bones. Toads (蟾蜍),a big problem inthe north of Australia, are suffering from painful arthritis in their legs andbackbone, a new study has shown. The toads that jump the fastest are morelikely to be larger and to have longer legs. (46)

The large yellow toads,native to South and Central America, were introduced into the north-easternAustralian state of Queenslandin 1935 in an attempt to stop beetles and other insects from de-stroyingsugarcane crops. Now up t0 200 million of the poisonous toads exist in thecountry, and they are rapidly spreading through the state of Northern Territory at a rate of up t0 60 kma year. The toads can now be found across more than one million squarekilometers. (47) A Venezuelanpoison virus was tried tin the 1990s but had to be abandoned after it was foundto also kill native frog species.

The toads have severelyaffected ecosystems inAustralia.Animals, and sometimes pets, that eat the toads die immediately from theirpoison, and the toads themselves eat anything they can fit inside their mouth._ (48)

A co-author of the newstudy, Rick Shine, a professor at the University of Sydney,says that lit-tle attention has been given to the problems that toads face.Rick and his colleagues studied nearly 500 toads from Queenslandand the Northern Territoryand found that those in the latter state were very different. They were active,sprinting down roads and breeding quickly.

According to the results ofthe study, the fastest toads travel nearly one kilometer a night. (49) But speed and strength come at aprice-arthritis of the legs and backbone due to con-stant pressure placed onthem.

Inlaboratory tests, the researchers found that after about 15 minutes of hopping,arthritic toads would travel less distance with each hop (跳跃). _ (50) These toads are so programmedto move~ apparently, that even when in pain the toads travelled as fast and asfar as the healthy ones, continuing their constant march across the landscape.

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请帮忙给出每个问题的正确答案和分析，谢谢！

Toads Are Arthritis and in Pain

Arthritis is an illness that can cause pain and swelling in your bones. Toads， a big problem in the north of Australia， are suffering from painful arthritis in their legs and backbone， a new study has shown.

The toads that jump the fastest are more likely to be larger and to have longer legs.__________ （46）

The large yellow toads， native to South and Central America， were introduced into the north-eastern Australian state of Queensland in 1935 in an attempt to stop beetles and other insects from destroying sugarcane crops. Now up to 200 million of the poisonous toads exist in the country，and they are rapidly spreading through the state of Northern Territory at a rate of up to 60 km a year.

The toads can now be found across more than one million square kilometers. __________ （47） A Venezuelan poison virus was tried in the 1990s but had to be abandoned after it was found to also kill native frog species.

The toads have severely affected ecosystems in Australia. Animals， and sometimes pets， that eat the toads die immediately from their poison， and the toads themselves eat anything they can fit inside their mouth. __________ （48）

A co-author of the new study， Rick Shine， a professor at the University of Sydney， says that little attention has been given to the problems that toads face. Rick and his colleagues studied nearly 500 toads from Queensland and the Northern Territory and found that those in the latter state were very different. They were active， sprinting down roads and breeding quickly.

According to the results of the study， the fastest toads travel nearly one kilometer a night.__________（49） But speed and strength come at a price——arthritis of the legs and backbone due to constant pressure placed on them.

In laboratory tests， the researchers found that after about 15 minutes of hopping， arthritic toads would travel less distance with each hop （跳跃） . __________ （50） These toads are so programmed to move， apparently， that even when in pain the toads travelled as fast and as far as the healthy ones， continuing their relentless march across the landscape.

回答（46）题 查看材料

A.But this advantage also has a big drawback——up to 10% of the biggest toads suffer from arthritis.

B.The task now facing the country is how to remove the toads.

C.But arthritis didn"t slow down toads outside the laboratory.

D.Toads with longer legs move faster and travel longer distances while the others are being left behind.

E.Toads are not built to be road runners——they are built to sit around ponds and wet areas.

F.Furthermore， they soon take over the natural habitats of Australia"s native species.