Many objects in the universe are invisible ，but they send radio waves．The radio telescope *thus appeared，and it is considered one of the greatest inventions in the twentieth century．Reber built the world's first radio telescope in 1937．Ryle and Hewish developed radio telescope systems for the location of weak radio sources，and they shared the Nobel Prize for Physics in 1974．

    A radio telescope is usually made up of：

    •One or more antennas to collect the radio waves．Most antennas are made in the shape of a dish to collect and reflect *the radio waves to the sub﹣reflector，in the same way as a curved mirror focuses visible light to one point．

    •A receiver and amplifier to receive the radio waves from the sub﹣reflector，and make these weak radio waves strong enough to be recorded and turned into electronic signals *．To make an amplifier sensitive enough，it is usually cooled to very low temperatures（e．g．as low as ﹣270℃）．

    •A recorder to keep a record of the electronic signals．Most radio telescopes today keep the signals to the computer's memory disk for astronomers to analyze later．

    Radio wavelengths are much longer than those of visible light．and the radio waves from deep space are always weak．To catch these waves，radio telescopes usually have huge antennas．The sizes of most antennas in use today are around 50 to 300 metres in diameter． The antenna of FAST in Guizhou，China，the latest and largest radio telescope in the world，is 500 metres in diameter，as large as the size of 30 football fields．

    To avoid interferences， and keep the telescopes sensitive，radio telescopes are built in places where there are no human radio waves or electronic signals．For example，FAST is 5 kilometres away from the closest village and 25 kilometres away from the nearest town．

    Radio telescopes create pictures of the sky，not in visible light， but in radio waves．This is extremely useful，because there are objects that can't be seen，objects that we wouldn't even know were there without radio telescopes．

（1）Radio telescopes help collect　　from the universe．

A．light

B．objects

C．radio waves

D．visible signals

（2）Most antennas of radio telescopes are made in the shape of a dish to　　．

A．make the antennas strong enough

B．increase the number of radio waves

C．turn radio waves into electronic signals

D．focus radio waves on the sub﹣reflector

（3）The underlined word "interferences" in the passage refers to　　．

A．the noises made by villagers and animals

B．the sounds from the radios and televisions

C．the people who go to Guizhou to watch FAST work

D．the radio waves and electronic signals from humans

（4）What have we done with the help of radio telescopes？　　

A．We have received pictures of deep space．

B．We have discovered unknown lives in the universe．

C．We have found some unknown objects in the universe．

D．We have turned the radio waves from space into light．

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