题目

DNA分子的双链结构中，排列在外侧、组成基本骨架的成分是（ ） A．脱氧核糖和碱基 B．脱氧核糖和磷酸 C．全是碱基 D．全是脱氧核糖 答案：解：由以上分析知，脱氧核糖和磷酸交替排列在DNA分子的双链结构的外侧，组成了DNA分子的基本骨架． 故选：B．Where should an adventurous tourist go? After you’ve done sightseeing in London, shopping in New York, enjoyed the local food in Paris, and danced to your heart’s content at the Brazilian carnival, where else can you go? What attractive tourist destination awaits you?Well, Antarctica sounds like the holiday of a lifetime! It's considered the last great wilderness on Earth. Just a few scientists in research stations share the icy landscape with penguins and other animals which can struggle with the low temperatures.Tourism began in Antarctica in the 1950s and it's still small part. About 37,000 tourists are expected there this season, but many won't even leave the boat.The BBC’s Juliet Rix visited the frozen continent and asked herself if she should be there at all, causing potential problems to such a sensitive environment. Her tour guide admitted that all visitors leave a footprint and they all go to the same places, the accessible coastline, which is also where the penguins and seals go to raise.But some people believe that if carefully controlled, tourism can be good for Antarctica. It has no native population and it needs advocates. Visitors to the icy continent might be ready to support and even to fund its preservation. And they're likely to engage in the discussion about global warming, which has led to the melting of glaciers.According to Rix, guidelines are followed when you’re about to set foot in Antarctica and tourists have to disinfect（消毒）their boots to make sure no alien species are introduced.And once on land, there's no eating or smoking. Rocks, bone fragments—nothing should be taken as a souvenir and nothing should be left behind.Tourists fortunate enough to visit the Antarctic must be aware that this is not their home and keep their fingers crossed that future generations will also be able to enjoy such breathtaking views.1.Who lives in Antarctica?A. 37,000 tourists.B. The BBC's Juliet Rix.C. A few scientists and animals.D. People in London and Paris.2.Why can tourism be good for Antarctica?A. People can bring some animals into it.B. People may take interest in the protection of it.C. People can give advice to the native population.D. People will go to the coastline to play with the seals.3.What are the guidelines when you go on the shore?A. You can leave rubbish on the shore.B. You can smoke and eat on the shore.C. You can take something as souvenirs.D. You can help to protect the environment.4.What is the author’s attitude towards the tourists going to Antarctica?A. Positive. B. Ambiguous.C. Subjective. D. Negative.