The place is England. The year is 1928. One of the founding theorists of quantum mechanics , Paul Dirac, is scratching his head because solutions to his equations have _ unexpected results. For the solutions to make sense, he reasons, there must be a particle that has the mass of an electron but the opposite charge. At the time, such a thing was not known to exist. Several years pass before American physicist Carl Anderson observes a "positive" electron, or positron that confirms Dirac's prediction. Antimatter , as the name implies, can be described as the opposite of ordinary matter. Every particle in the universe has characteristics such as mass and charge. With antimatter, the mass remains constant, but the sign of the charge is reversed. All particles have an antimatter counterpart , even the chargeless neutron . Unlike matter, antimatter is not common. Unless you're in the upper atmosphere, or inside a particle accelerator, you're not going to come across it. "Antimatter was not always so rare," Stephane Coutu, Penn State particle physicist says. There was a time when it was as prevalent as matter itself. "Right after the Big Bang ," Coutu explains, "we believe there must have been exactly the same amounts of matter and antimatter...and yet owing to some small asymmetry in the laws of particle interactions, all of the antimatter and most of the matter in the early universe was annihilated . We are left today with the resulting matter-dominated universe." Science fiction is rife with tales of high-energy particle annihilation, and indeed, antimatter weapons have appeared in current bestselling novels. This is unrealistic, Coutu says. "[It] would be very impractical owing to very great difficulties in producing and maintaining significant amounts of antimatter." Technology that uses the properties of antimatter is actually feasible outside of science fiction, however. Positron emission tomography (PET) is a medical technique that can be used to detect cancer, measure blood flow and detect coronary... The main idea of the passage is _ . A) how antimatter was discovered B) the properties of antimatter C) where does antimatter come from D) what antimatter is and its potential application
D
(Question)
It never occurred to Sun Yukun that the decision he made four years ago would have an impact on his career. When the 22-year-old entered college in 2009, he decided not to change his rural residence to a students' collective one. But when he finished college and was offered a job with a state-owned enterprise in Beijing, Sun was told that he couldn't accept the offer unless he had an urban hukou (household registration record). This time, he had no choice but to change his residence status. Transferring hukou to a university became optional in 2003, and many students are confronted with the dilemma of whether to do so or not. Professionals suggest they make the decision based on their current situation and future plans. 'I regret transferring my hukou' Wang Jinbi, 20, is an accounting major at Beijing Union University. Coming from Chifeng, Inner Mongolia autonomous region, she transferred her hukou when she enrolled at university. "I didn't think it was a big deal," Wang says. "Since I'm registering under an urban hukou, it doesn't matter whether it's in Beijing or Inner Mongolia, I thought." What Wang didn't expect, however, is that she would regret her decision later. "After two years of study, I've figured out my future plans. I want to return to my hometown and make a living there," she says. That means Wang needs to transfer her hukou back again, which she worries will be a troublesome procedure. "I have a friend who graduated last year. She spent a lot of time and energy transferring her hukou back to her hometown again due to complicated paperworks," says Wang. Guidelines for transferring hukou Wang's experience is not uncommon. Many students don't know what their decision means for their future. In order to help these students, Xie Yongqiang, from the Chengdu Municipal Bureau of Justice, posted a guideline for transferring hukou on a micro blog. According to Xie, students should firstly think about where they're going to stay. "If you like the city where you're studying and are considering staying... How many examples are mentioned in the passage? A) Two. B) Three C) Four. D) Five.
(Answer)
B
It was reported last week that developers could take photos from Apple mobile and Google Android devices without the phone owners knowing that the images were being taken. In Apple's case, developers can also obtain the location information for each photo. Senator Charles Schumer said in a telephone interview that his office had spoken with officials at both Apple and Google on Monday. "We asked them if they could find a way on their own to prevent Apple from having access to private information," Mr. Schumer said. "They were friendly and open to the idea that this ought to be changed." On Sunday, Mr. Schumer said that he planned to send a letter to the Federal Trade Commission asking the agency to investigate Apple and Google after the privacy concerns came to light. Claudia Bourne Farrell, an F.T.C. spokeswoman, said the agency had received the letter but she could not comment further. "It worries people to think that one's personal photos, address book, and who knows what else can be obtained and even posted online without permission," Mr. Schumer wrote in his letter to the F.T.C. "If the technology exists to open the door to this kind of privacy invasion , then surely technology exists to close it, and that's exactly what must happen." Mr. Schumer said if Apple and Google could not come to an agreement to fix the problem, then he would be forced to take the issue further. He said other companies had been willing to work with his office to fix issues. "I'm optimistic that we can get this changed without any regulation," he said. "If it's not changed, then we'll turn to the F.T.C., and if that doesn't work then we'llconsider legislative approach." The F.T.C. has warned companies to try to be more vigilant in their efforts to protect consumers when it comes to privacy. Where can we read about the passage? A) In a science report. B) In a magazine C) In a newspaper. D) In a textbook.
C