题目内容
For more than thirty years after astronauts first set foot on the Moon, scientists have been unable to unravel the mystery of where the Earth’s only satellite came from. But now there is direct evidence that the Moon was born after a giant collision between the young Earth and another planet. Previous studies of rocks from the Earth and the Moon have been unable to distinguish between the two, suggesting that they formed from the same material. But this still left room for a number of theories explaining how—for example, that the Moon and Earth formed from the same material at the same time. It was even suggested that the early Earth spun so fast it formed a bulge that eventually broke off to form the Moon. Franck Poitrasson, and his colleagues at the Swiss Federal Institute of Technology have compared Moon rocks with rocks from Earth and discovered a surprising difference. They analysed the weight of the elements present in the rock using a highly accurate form of mass spectroscopy(光谱研究) that involves vaporising a sample by passing it through an argon (氩) flame. Although they appeared very similar in most respects, the Moon rocks had a higher ratio of iron-57 to iron-54 isotopes(同位素)than the Earth rocks. "The only way we could explain this difference is that the Moon and the Earth were partly vaporised during their formation," says Poitrasson. Only the popular "giant planetary impact" theory could generate the temperatures of more than 1700℃ needed to vaporise iron. In this scenario, a Mars-sized planet known as Theia crashed into Earth 50 million years after the birth of the Solar System. This catastrophic collision would have released 100 million times more energy than the impact believed to have wiped out the dinosaurs—enough to melt and vaporise a large portion of the Earth and completely destroy Theia. The debris from the collision would have been thrown into orbit around the Earth and eventually coalesced to form the Moon. When iron is vaporised, the lighter isotopes burn off first. And since the ejected debris that became the Moon would have been more thoroughly vaporised, it would have lost a greater proportion of its lighter iron isotopes than Earth did. This would explain the different ratios that Poitrasson has found. What can we infer from the passage
查看答案
搜索结果不匹配？点我反馈
更多问题
Many students find the experience of attending university lectures to be a confusing and frustrating experience. The lecturer speaks for one or two hours, perhaps (61) the talk with slides, writing up important information on the blackboard, (62) reading material and giving out (63) The new student sees the other students continuously writing on notebooks and (64) what to write. Very often the student leaves the lecture (65) notes which do not catch the main points and (66) become hard even for the students to understand. Most institutions provide courses which (67) new students to develop the skills they need to be (68) listeners and note-takers. (69) these are unavailable, there are many useful study-skills guides which (70) learners to practice these skills independently. In all cases it is important to (71) the problem before actually starting your studies. It is important to (72) that most students have difficulty in acquiring the language skills (73) in college study. One way of (74) these difficulties is to attend the language and study-skills classes which most institutions provide throughout the (75) year. Another basic strategy is to find a study partner with whom it is possible to identify difficulties, exchange ideas and provide support. Part Ⅳ ClozeDirections: In this part, there is a passage with 15 blanks. For each blank there are 4 choices marked A, B, C and D. Choose the best answer for each blank and mark the corresponding letter with a single bar across the square brackets on your machine-scoring ANSWER SHEET.
We have to go _____ the rules.
利用问卷调查培训课程的优点在于，调查结果可间接取得，而且问卷设计、分析工作难度不大。
I’d been living with my wife for eight years and one night. Morn says, "I guess you guys are never going to get married. I mean, you’ve been through jail together, you’re living together, but…, oh, forget it." "Oh, well," I said," put it like that and I’ll marry your daughter tomorrow." Actually, I don’t know what we were waiting for, except that for a guy it’s never the right time to get married. I’ m also suspicious of any two people who don’t struggle with that decision. Part of my problem was that I was still lusting in my heart after other ladies. But somehow I knew that I wasn’t going to find another woman remotely as great as my soon-to-be wife. It’s a good thing my mother-in-law finally spoke up. I finally gathered my courage one day when we were having a picnic, and popped the question. I also gave my wife a big tourist pamphlet about Switzerland. I wasn’t taking any chances. She said no. It killed me. I felt sick to my stomach. I lost my appetite. Our dog just stared at me, thinking, "If you’re not going to eat your lunch, I will." Finally, I said, "But the Switzerland trip is yours if you say yes." "Switzerland , "she said, "is filled with precise, humorless people." "Maybe I should have suggested Paris" For a minute it seemed as if my change in travel plans would rate a solid "maybe". But she said no again. When we woke up the next morning, she told me that she’d slept on my proposal. "I guess I was a little rude to you last night," she explained. Meanwhile, I’m figuring I’m off the hook for this marriage thing for at least another eight years. I could afford to be generous. "I asked, you said no. It’s okay," I said. I might have looked a little too relieved because later that day she gave me a little box. Inside was a gold watch. On the back was inscribed. "Yes. I’ve reconsidered." I liked the watch, so I did the right thing. The last sentence "I did the right thing" implied he ______.
微信支付 
支付宝支付