【双向选择题】当南极圈出现极昼时,下列叙述正确的是

The advent of Group Buying is an expression of meets commonalities of society, the existence of it because it is a win-win two-way selection for enterprises and markets. The Group Buying is the most frequently used type for ordinary consumers to concentrate purchase, on the one hand, they can get The most satisfactory valuable goods by paying the lowest money; on the other hand, they can also be surprised in sales service. Therefore, as for consumers, the Group Buying is a shopping form which they would fain adopt and to be used often. To observe from the angle of business operation, the group purchase means to buy goods on a large scale and in batches. Not only reduce operational cost, but also relieve the pressure from sell. To accelerate the speed of cash flow, this especially is good for those emerging enterprises, they would fain adopt such selling style.
Online Group Buying had already became an improtant consuming behavior, the progress of the project which is the Online Group Buying is good for consumers, dealers, and manufacturers. Group buying websites had became the best organizational form because of their own advantages. Online Group Buying have it own characteristic relative to other general projects, moreover, its participators have their own characteristic, too. Although the Online Group Buying is loved by many consumers and merchants, the Online Group Buying is at the initial stage of development, it still exposed a lot of problems and risks. The major risks of the Online Group Buying which is from consumers, organizers, suppliers, network security and policies and regulations, etc. To manage the risks, to success of the Online Group Buying, to make sure the maximum benefit and balance of interest for the trilateral roles in the Online Group Buying which are comsuers, organizers and suppliers is very important, it also is good for the healthy development of the Online Group Buying in our country.
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正确答案是B和D
A黑海海峡：地中海、黑海
C白令海峡：太平洋、北冰洋

AC,巴西地形以高原为主

BC