下列物质的变化规律与共价键的键能大小有关的是（）
A．F2、Cl2、Br2、I2的熔点、沸点逐渐升高
B．HF、HCl、HBr、HI的热稳定性依次减弱
C．NaF、NaCl、NaBr、NaI的熔点依次降低
D．沸点H2O>H2S，NH3>PH3
答案：B
共价键的键能大小一般影响的是物质的化学性质，而不是物理性质。对于组成和结构相似的分子，其熔点一般随相对分子质量的增大而升高，但由于水和氨气中含有氢键，所以其沸点比较高。选项C中均是离子化合物，不存在共价键。所以答案是B。
Passage Four
| The face of the 21st century is already growing in a laboratory. Getting a piece of the new look could soon be as simple as writing a cheque. Scientists in recent years have made giant leaps in the artificial production of skin, bones and tissue. While their research has been motivated by a desire to help accident and medical victims, their work is about to go commercial. The burgeoning (萌芽) cosmetic surgery market has snapped up the technological advances. By the turn of the 21st century, changing your face or improving your body will be limited not by your imagination or desire, but by the size of your bank account. And there is even work being clone on that, with the costs of cosmetic surgery being cut to make it affordable and accessible for the average woman and her partner. "It’s no longer a vanity thing, it’s simply making use of the available technology to improve those parts of the body you might not be happy with," Cindy Clovetti, a Toronto-based skin and beauty care expert, said. "People who 10 years ago said they would never use a computer and would never get a boob job (胸部整形手术) are now surfing the web getting the latest information for their next operation. " Latest figures in the United States indicate the number of patients receiving cosmetic surgery in 12 months will top the magic million within two years (there were 850 000 last year), while the number of men seeking image-improving operations has increased 35 percent in the past four years. Breast implants are now very much a bread-and-butter job for many cosmetic surgeons and the big advances have been made in the development of bone implants which can produce instant high cheek bones, sculpture better shaped noses and ears and give men the chisel-shaped jaw that is always a sure-fire (必定成功的) chick-magnet (吸引女人的东西). British futurologist Ian Pearson speculates that by 2020, up to 96 percent of body weight will be replaceable with the brain being the only organ not interchangeable. "By 2020 you could have a new face, or new skim. and by 2030 a fully working replacement body part. By the end of the 21st century, people will be able to get an entirely new body. " |
According to Ian Pearson, ______ .
A．brain will be replaceable by the end of the 21st century
B．the entire body can be replaced by 2030
C．people will be able to get a fully working replacement body part by 2020
D．people will be able to have a new face and skin by 2020