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对于有负债的企业，β资产大于β权益。（）
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Don’t Count on Dung "Conservationists(自然保护主义者)may be miscalculating the numbers of the threatened animals such as elephants, " say African and American researchers. The error occurs because of a flaw in the way they estimate animal numbers from the piles of dung(粪)the creatures leave behind. The mistake could lead researchers to think that there are twice as many elephants as there really are in some regions according to Andrew Plumptre of the Wildlife Conservation Society(WCS) in New York. Biologist Katy Payne of Cornell University in Ithaca, New York, agrees. "We really need to know elephant numbers and the evidence that we have is quite indirect, "says Payne, who electronically tracks elephants Counting elephants from planes is impossible in the vast rainforests of Central Africa. So researchers often estimate elephant numbers by counting dung piles in a given area. They also need to know the rate at which dung decays because it’s extremely difficult to determine these rates. However, researchers counting elephants in one region tend to rely on standard decay rates established elsewhere. "But researchers at the WCS have found that this decay rate varies from region to region depending on the climate and environment. Using the wrong values can lead the census astray(离开正道)," says Plumptre. He and his colleague Anthony Chifu Nchanji studied decaying elephant dung in the forests of Cameroon. They found that the dung decayed between 55 and 65 per cent more slowly than the dung in the rainforests of neighbouring Gabon. If researchers use decay rates from Gabon to count elephants in Cameroon, they would probably find more elephants than are actually around. "This could mean estimates in Cameroon are at least twice as high as those derived from decay rates calculated locally," says Plumptre "However accurate your dung density estimate might be the decay rate can severely affect the result." Plumptre also says that the dung-pile census should be carried out over a region similar in size to an elephant’s natural range. The usual technique of monitoring only small, protected areas distorts numbers because elephants move in and out of these regions, he says" If the elephant population increases within the protected area, you can not determine whether it is a real increase or whether it is due to elephants moving in because they are being poached(入侵偷猎)outside. " Plumptre says that similar problems may also affect other animal census studies that rely on indirect evidence such as nests, tracks or burrows(地洞). Piles of dung can’t be relied upon when it comes to estimating elephant numbers because
某企业准备购入A股票，预计5年后出售可得3500元，该股票5年中每年可获现金股利收入400元，预期报酬率为12%。则该股票的价值为3427.82元。（）
Dancing in the Streets If there is one thing certain to get Brazilians on their feet, it is the Rio Carnival (狂欢节). Held in Rio de Janeiro, the country’s biggest city, the carnival began on February 20 when the mayor gave key of the city to Rei Momo-the Lord of Misrule (无序之皇) On his orders, each year people turn the city into a paradise of dance and music. The following six days are so fun of parades, street dancing, fantastic clothes and partying (聚会) that many people forget about eating and sleeping. "It was the passion of the carnival that attracted me to Brazil and made me settle down in Rio. " said Bob Nadkarni, a British man who has lived in the city for several years. For many Brazilians, the centerpiece of the carnival is samba (桑巴舞) , a typical Brazilian dance. Every year, tens of thousands of visitors and locals show off their passion and energy in the streets, following the beat (节拍) of the Latin music. The climax to this street party is the float(彩车) parade, in which floats decorated with tons of fresh flowers by various samba schools and local communities move through the city. On the top of each float stands the candidate for the Drum Queen, who is chosen at the end of the party. While most people are free to enjoy the celebrations. Rio’s police officers have to keep a clear head. Following the murder of three officers in a gunfight early last week, the Brazilian Government has tightened security in Rio. The street fighting, robbery and sex crimes that accompany the carnival are very difficult to police. Carnivals began in ancient Rome as a celebration at which people fed wild wolves, in honor of the city’s founder who was said to have been raised by a she-wolf. Brazil gave new life to this tradition and so despite the troubles, the carnival will remain a symbol of the country’s culture. The word "centerpiece" in the 3rd paragraph means ______.
对于两种证券形成的投资组合，当相关系数为1时，投资组合的预期报酬率和标准差均为单项资产的预期报酬率和标准差的加权平均数。（）
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