题干

下列关系式中,正确的是(   )

A:ϕ{0}

B:0{0}

C:0{0}

D:ϕ={0}

上一题 下一题 0.0难度 选择题 更新时间:2019-05-22 12:01:32

答案(点此获取答案解析)

C

同类题1

阅读理解

    Several days ago, Brenda had a car accident that led to one of her legs being cut off. Since then she didn't talk to anyone."I wish I could bring her friends to visit her," said Brenda's mother. "But it's a long bus trip." The nurse smiled, "Don't worry. We have a plan."Later that day, the nurse had taken Brenda to another room. "Here's your new roommate, Annie Wiggle-Do," the nurse introduced a dark-hair teenager on the other bed.

    As soon as the nurse left, she jumped out of her bed with her only foot and sat at the other end of Brenda's bed, "I lost my leg from bone cancer," she said. "What happened to yours?" Brenda was so shocked that she couldn't say a word. "You're lucky." Annie continued. "You've still got your knee. They had to take mine."

    "I'd like to have a chat with you, but my friends are coming any time now, so I have to get ready." Annie said when she took off her hair! Her head was completely bald(秃头的).

    "Oh, I forgot to tell you, the medicine they gave me to kill the cancer also killed my hair." Annie looked out her wigs(假发), brown and yellow, short and long, straight and curly."That's why I thought up 'Annie Wiggle-Do'." Annie smiled. "Get it? Any wig will do? Annie Wiggle-Do?" "When Annie's friends came, she introduced Brenda to them all. Before long, Brenda started chatting with Annie and her friends. They didn't make her feel like a strange person at all!

    The girls shared their names with each other. When it was time to go to bed, Brenda said, "Good night, Annie-Wiggle-Do. Can't wait till morning."

同类题4

阅读理解

    Life may have evolved on at least three planets within a newly discovered solar system 39 light years from Earth. Astronomers at the NASA have discovered no less than seven roughly Earth-sized worlds orbiting a dwarf star in the system. Scientists had previously identified a tiny number of "exoplanets", which are believed to have the qualities needed to support life. However, the new system contains an unprecedented(前所未有) number of Earth-sized, probably rocky planets, and is being acknowledged as an "accelerated leap forward" in the search for extraterrestrial (外星球的)life.

    Three of the new planets are said to be particularly promising because there might exist oceans. Thomas Zurbuchen, associate administrator of NASA, told a press conference in Washington: "This gives us a hint that finding a second Earth is not a matter of 'if', but 'when'."

    The planets were discovered using NASA's Spitzer Space Telescope, which was able to track how fast each of the planets crossed the star Trappist-l and completed an orbit. From this the research team calculated how far the planets were from their star, and therefore how likely they are to be habitable.

    NASA's Hubble Space Telescope is already being used to search for atmospheres around the planets. Future telescopes, including the proposed European Extremely Large Telescope and the James Webb Space Telescope, may be powerful enough to discover markers of life, such as oxygen in the atmospheres of exoplanets.

    Astronomers believe there could be as many as 40 billion potentially habitable worlds in our galaxy, the Milky Way. Prof Zurbuchen said that now was a "gold-rush phase" in the search for these exoplanets.

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