问题 选择题

2012年7月24日,我国最南端的地级市——三沙市在永兴岛正式成立,管辖西沙群岛、南沙群岛、中沙群岛的岛礁及其海域。图1为南海附近区域图。据此回答题。

小题1:三沙市成立时

A.三沙市的自转线速度慢于北京市

B.去南极科考的最佳时期

C.三沙市白昼时间短于威海市

D.地球公转速度最慢小题2:关于三沙市说法正确的是

A.一年有一次阳光直射

B.夏至日受到阳光直射

C.一年有两次阳光直射

D.春分、秋分时受到阳光直射

答案

小题1:C

小题2:C

题目分析:

小题1:三沙市的纬度比北京低,所以三沙市的自转线速度快于北京市;7月份是南极的极夜,且温度最低,并不是最佳考查期;此时地球位于远日点附近,地球公转速度较慢;但此时太阳直射北半球,三沙市的纬度低于威海市,所以三沙市白昼时间短于威海市。故选C。

小题2:因三沙市位于赤道和北回归线之间,所以一年中有两次直射;而夏至日太阳直射北回归线,春秋分太阳直射赤道。故选C。

点评:本题结合实例考查地球自转的速度、公转的速度、昼夜长短及太阳直射点的位置,试题难度中等,解题关键是掌握地球自转和公转的速度的变化规律,昼夜长短的变化规律,太阳直射点的移动规律。

单项选择题

Mark Twain once observed that giving up smoking is easy. He knew, because he’d done it hundreds of times himself. Giving up for ever is a trifle more difficult, apparently, and it is well known that it is much more difficult for some people than for others. Why is this so

Few doctors believe any longer that it is simply a question of will power. And for those people that continue to view addicts as merely "weak", recent genetic research may force a rethink. A study conducted by Jacqueline Vink, of the Free University of Amsterdam, used a database called the Netherlands Twin Register to analyze the smoking habits of twins. Her results, published in the Pharmacogenomics Journal, suggest that an individual’s degree of nicotine dependence, and even the number of cigarettes he smokes per day, are ply genetically influenced.

The Netherlands Twin Register is a voluntary database that contains details of some 7,000 pairs of adult twins (aged between 15 and 70 ) and 28,000 pairs of childhood twins. Such databases are prized by geneticists because they allow the comparison of identical twins (who share all their genes) with fraternal twins (who share half). In this case, however, Dr. Vink did not make use of that fact. For her, the database was merely a convenient repository of information. Instead of comparing identical and fraternal twins, she concentrated on the adult fraternal twins, most of whom had completed questionnaires about their habits, including smoking, and 536 of whom had given DNA samples to the register.

The human genome is huge. It consists of billions of DNA "letters", some of which can be strung together to make sense (the genes) but many of which have either no function, or an unknown function. To follow what is going on, geneticists rely on markers they have identified within the genome. These are places where the genetic letters may vary between individuals. If a particular variant is routinely associated with a particular physical feature or a behavior pattern, it suggests that a particular version of a nearby gene is influencing that feature or behavior.

Dr. Vink found four markers which seemed to be associated with smoking. They were on chromosomes 3, 6, 10 and 14, suggesting that at least four genes are involved. Dr. Vink hopes that finding genes responsible for nicotine dependence will make it possible to identify the causes of such dependence. That will help to classify smokers better (some are social smokers while others are physically addicted) and thus enable "quitting" programs to be customized.

Results such as Dr. Vink’ s must be interpreted with care. Association studies, as such projects are known, have a disturbing habit of disappearing, as it were, in a puff of smoke when someone tries to replicate them. But if Dr. Vink really has exposed a genetic link with addiction, then Mark Twain’s problem may eventually become a thing of the past.

The ultimate purpose of Dr. Vink’ s research is to()

A.identify all the genes that are responsible for smoking

B.determine the real cause of nicotine dependence

C.make a difference between social smokers and other smokers

D. help different smokers give up smoking more effectively

单项选择题