Scientists have been studying Antarctica for over a century，but details as basic as what it looks like beneath all that ice have largely remained a mystery.Now，Earther reports that a team of scientists from Denmark，Norway，the Netherlands，and the UK has published the most detailed data yet on the continent's subglacial topography （冰川下的地形）near the South Pole，
   As they report in the journal Geophysical Research Letters，central Antarctica is home to three large canyons （峽谷），one of which is deeper than the Grand Canyon and nearly as wide at some points.The researchers made the discovery by flying a plane with radar over the South Pole，a spot that isn't covered by satellites.They expected to find mountains beneath the ice sheet，but the wide canyons they found between the mountains came as a surprise.
   Of the three canyons，two hadn't been documented previously.The largest，the Foundation Trough（基礎(chǔ)槽），measures 218 miles long，up to 22 miles wide，and 6，260 feet deep，putting it up there with the planet's most impressive canyons.
   The discoveries are significant on their own，but the real purpose behind the research is to better understand how the West and East Antarctic ice sheets will react to rising temperatures.Human-caused climate change has made some of the continent's ice not firm，and the West Antarctic ice sheet especially has been slowly melting to the sea.If patterns continue，the coastal glaciers supporting the large ice sheets could fall down，causing sea levels to rise a minimum of 10 feet.If this happens，the canyons could be a major factor in the speed and direction of ice flow from central Antarctica to the coast.
   The event isn't likely to happen in the near future，but further study of Antarctica's topography will allow scientists to better predict when it might.

（1）Which of the following have scientists known little？

D

D

A．The shape of Antarctica ice.
B．The condition of Antarctica ice.
C．The Grand Canyon.
D．The beneath of Antarctica ice.
（2）Which of the following is found by a plane with radar？

C

C

A．The Grand Canyon.
B．The mountains.
C．Three large canyons.
D．Ice sheets.
（3）How do the scientists feel about finding the wide canyons？

A

A

A．Unexpected.
B．Interesting.
C．Ridiculous.
D．Common.
（4）What's the aim of the study？

C

C

A．To document the three canyons.
B．To find out how large the three canyons are.
C．To know how ice sheets react to rising temperatures.
D．To show the importance of the three canyons.