题目内容：

    China's Five-hundred-meter Aperture Spherical Radio Telescope(FAST)has detected a repeating fast radio burst(FRB)-mysterious radio signals from outer space-for the first time, Science and Technology Daily reported.

Scientists on the FAST project with the National Astronomical Observatories of China(NAOC)revealed the news last Wednesday. The FRB originated some three billion lightyears away from Earth. Other factors including aircraft and satellites have been dismissed and cross examination is being carried out, the scientists said.

FRB has since become one of the hottest topics in astronomy. It was not until 2007 when the first FRB was discovered by humans. Fewer than 100 FRBs have been detected internationally. There is still no reasonable explanation for the origin of FRB in the international scientific community at present. FRBs mostly only appear once, which makes them very hard to track.

The FRB detected by FAST's real-time detection terminal(终端), however, is one that has been observed before, said Zhang Xinxin, an assistant engineer with the NAOC. Known as FRB121102,it was first discovered in 2012 and found to repeat in 2015.Analysis of data later located the source of the signal coming from a dwarf galaxy(矮星系) three billion light years away. The first pulse from FRB121102 was spotted by FAST on Aug 30 2019.After this, the telescope recorded dozens of pulses from the FRB over the course of days. On Sept 3 2019 alone, more than 20 pulses were detected.

The number of mysterious bursts detected so far is too small to draw any conclusions, Zhang said. FAST, the world's largest single-dish radio telescope, has a certain edge in detecting repeated FRBs. This is because the 19-beam receiver installed on FAST, covering frequency ranges of 1.05-1.45 GHz, is very sensitive to radio signals, Zhang said.

1.The whole text mainly gives us an introduction to________.

A.a brief introduction of FAST. B.a discovery of FAST

C.the validation of FAST D.the usage of FAST

2.Which of the following statements is TRUE?

A.FRB121102 is the first fast radio burst that was discovered by humans.

B.The FRB detected by China's FAST this time has not been observed before.

C.FRBs mostly only appear once, which makes them very hard to track.

D.We can infer that billion-light year is a term of time in astronomy.

3.Aperture Spherical Radio Telescope(FAST)/_______

A.is the world's largest radio telescope

B.has detected more than 100 FRBs

C.found reasonable explanation for the origin of FRB

D.has been installed with the 19-beam receiver