题干

如图是人和动物细胞结构模式图,根据图回答问题:

图中①是____ ,功能是____ .图中③是____.功能是____ .

上一题 下一题 0.0难度 选择题 更新时间:2015-12-02 09:16:31

答案(点此获取答案解析)

细胞膜,控制物质的进出,细胞核,能传递遗传信息

同类题1

阅读理解

    There are more bicycles than residents in the Netherlands,and in cities

like Amsterdam and The Hague up to 70% of all journeys are made by bike.

    The BBC's reporter,Anna Holligan,examines what made everyone get back in the saddle(车座).

    Before World WarⅡ,journeys in the Netherlands were mainly made by bike, but in the 1950s and 1960s,as car ownership increased quickly,this changed.As in many countries in Europe, roads became increasingly crowded.

    The jump in car number caused a huge rise in the number of deaths on the roads.In 1971 more than 3,000 people were killed by motor vehicles,and 450 of them were children.In response a social movement demanding safer cycling conditions for children was formed.Called Stop de Kindermoord,it took its name from the headline of an article written by journalist Vic Langenhoff whose own child had been killed in a road accident.

    The Dutch love of the motor vehicle was also shaken by the Middle East oil crisis of 1973,when oil-producing countries topped export to the US and Western Europe.

    These twin pressures helped to persuade the Dutch government to invest in improving cycling infrastructure(基础设施)and the Dutch urban planners started to change from the road-building policies designed mainly for cars.

    To make cycling safer and more inviting,the Dutch have built a vast network of cycle paths.These are clearly marked,have smooth surfaces,separate signs and lights for those on two wheels,and are wide enough to allow cycling side by side and overtaking.

    Even before they can walk,Dutch children live in a world of cycling.As babies they travel in special seats on bikes.As the children grow up they ride their own bikes.And,as the Dutch are not allowed to drive until 18,cycling offers teenagers an alternative form of freedom.

    The state also plays a part in teaching,with cycling lessons a compulsory(必修的)part in Dutch schools.All schools have places to park bikes and at some schools 90% of pupils cycle to class.

同类题5

阅读理解

    When Carson Palmer, a professional American football player, hurt his arm a few years ago, he took a week off from throwing the football. But in his head, Palmer practiced every day. The following weekend, Palmer had the best game of his life.

    For more than a century, scientists have been trying to understand how this mental training works. In the 1930s, researchers proved by experiment that when you're imagining an action, your brain sends signals to your muscles(肌肉) which are too weak to tighten the muscles but might help train the body to perform. In other words, mental practice might create a pattern in your head, like an inner how-to guide for a particular skill.

    Sports psychologists have conducted hundreds of studies comparing imagined and physical practice for actions. On the whole, the research shows that mental training works. A 2012 study, for example, compared 32 amateur golfers who practiced hitting the balls to another 32 who merely held a golf club in their hands and visualized(想象)their swings. Under the same training rules, both groups improved their skills by getting the ball about 4 inches closer to the hole.

    Visualization has advantages over the real thing: You can do it anywhere, even when injured. It is safe-a major plus for high-risk performers such as gymnasts and surgeons. And you can practice for longer periods of time because you're not restricted by physical tiredness, That's not to say it's easy, we've had Olympic-level athletes sitting in our lab, visualizing the movements for two hours," says Tadhg Macintyre, a sports psychologist at the University of Limerick in Ireland. “When we're done, they're absolutely tired.”

    It doesn't work for everyone, though. "If you're a novice, the effect can be harmful,” warns Macintyre. If you're trying to visualize a free throw, and you don't even know the proper movement, then you're probably going to mentally practice the wrong skill.”