题目原文：
Scientists are considering the possibility of sending humans to Mars in the coming decades. Although there have been successful manned missions to the Moon in the 1960s and 1970s, Mars is 150 times further away from Earth than the Moon is. Thus the project of sending humans to Mars would require solving an array of problems the Moon missions did not have to face.
One problem is that a round-trip to Mars and back is likely to take at least two years. The trip to the Moon lasted only a few days, and it was easy to bring enough supplies of food, water, and oxygen; but the cargo capacity of space vehicles is too limited to put on board the food, water, and oxygen required by a crew for a period of two years. Without those essentials, though, a Mars mission is impossible.
A second problem is that astronauts on the Mars mission would be in the zero-gravity environment of space for many months at a time. Spending a long time in the zero-gravity environment has negative effects on the human body, such as decreased muscle mass and lower bone density. Over the course of a two-year mission, the effects would be so severe, they would make it impossible for humans to make the trip without experiencing grave medical problems.
Finally, astronauts on a mission to Mars would be exposed to dangerous levels of space radiation, much of which comes in the form of charged particles emitted by the Sun. Earth’s magnetic field, which normally protects us from dangerous solar radiation, would not be able to protect a spaceship traveling in interplanetary space. Constructing a shield that would protect the whole spaceship from space radiation is at present impossible because it would add too much weight to the ship.
题目音频：
写作真题第125套（rs050）
http://mp.weixin.qq.com/s?__biz=MzI3ODM5NzI3Mg==&mid=2247504601&idx=2&sn=ec3a3027dcaf8c40829699f003f0a91d&chksm=eb553aeedc22b3f86efcc7e10cc7bc6d0167dc528df66b96238b72eca6f489beb643fe2f62a8&scene=21#wechat_redirect
学术写作：
购物地点的选择
Professor Diaz
Do you think it is more beneficial for people to shop at small local stores (small or specialized stores with local owners, such as a camera shop or a small neighborhood grocery store) rather than at superstores (very large stores, typically owned by corporations that, that sell many kinds of different products)? Why or why not?
Kelly
Shopping at small local stores benefits consumers in many ways: better service.
Andrew
There are obvious benefits to shopping at superstores: a wide variety of products, usually at low prices.
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