题干

下列各图描述的实验中,用来说明声音的传播需要介质的是(   )

A:发声的音叉激起水花

B:音叉发出的声音越响,乒乓球被弹开的越远

C:钢尺伸出桌边的长度变短,振动时声音的音调变高

D:抽取玻璃罩内的空气,听到罩内的音乐声减小

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答案(点此获取答案解析)

D

同类题1

任务型阅读

    Humans use electricity to light up the night sky. But did you know that nature itself can glow, too?

    ____. Some use their lights to communicate. Others shine to hunt, to mate or to protect themselves. The vampire squid, for example, gives out a cloud of light to scare enemies.

    ____.

    In 2013, the US company Gleaux said it had created the world's first light-producing plant, reported the Daily Mail.

    ____.

    “People have dreamed about this stuff for many years,” said Alexander Krichevsky, the company's founder.

    He and other researchers are working toward a future in which glowing plants replace lamps and glowing trees line highways.____, making them glow to let farmers know when they need water or are ready to be picked.

    While GleauX is working on glowing plants, the French company Glowee is trying to use glowing bacteria to light up shop windows and street signs. It is the same type of bacteria that causes certain sea animals to light up.

    ____.The company is now working on a light that shines brighter, lasts longer and comes in different colors.

    “Our goal is to change the way we produce and use light,” said Glowee founder Sandra Rey. “We want to offer a global solution that will reduce the 19 percent of electricity consumption used to produce light.”

A. People are also creating glowing bacterial art that you can hang in your home

B. Scientists have found many glowing creatures, most of which live in the ocean

C. Krichevsky also hopes the technology could be used in crops

D. Researchers around the world are looking into nature's lights for new ideas

E. It is a genetically-modified plant that glows like fireflies do

F. In 2016, Glowee created a bacteria-powered light that glows for three days

G. This technology could help us save much energy

同类题2

选择合适的选项补全短文。

    I still remember that summer before college.There were plans and ideas about what my college experience was going to be like, but none of them worked out as planned.____.

    Use the mental health services available to you.

    That first night at college was memorable. There was scare and homesickness. Missing things from home wasn't the only reason why I felt down. The academic pressure to succeed and the social pressure to fit in are too much for some people, which don't just happen in the freshman year.____ Close friends always guided me, which was important because talking helps—even if it's just with a friend. Don't be afraid to take that extra help.

    ____

    I had been ready to major in politics, philosophy and economics, in preparation for a law degree.Things changed.

    You meet new people and discover new interests.____ So, don't worry if you haven't figured out exactly what you're going to major in. It will likely change anyway.

    You're there to get a degree, but a little fun won't hurt.

    As time goes by, I'm not going to remember the grades I got on papers or the late nights spent studying. Instead, lifelong memories will include playing video games with my roommate at 3:00 am, or late-night runs with my friends after a night out. Apart from doing well inside the classroom, there are also internships(实习期) and other pressures. Employers might weigh internships more heavily than your GPA.____.

A. It's OK to change your mind about your major.

B. You don't want to get tired of your college life early.

C. Everyone says that college is the best four years of your life.

D. Here are the things I wish I had known before my freshman year.

E. It's normal to be a little unsure of your plans once you start taking classes.

F. Getting internships and having fun with friends are also of great importance.

G. For me, there were upsets long after the days that required a map to go anywhere.