答案：C

　　B

　　A crack has formed in the shelf of floating ice in front of the Pine Island Glacier(PIG)．The surface crack in the PIG runs for almost 30 km，is 60 m deep and is growing every day.US space agency(NASA)researchers expect the eventual iceberg to cover about 880 sq km—an area the size of Berlin.It should break away in the near future.

　　The Pine Island Glacier is one of the largest and fastest moving tongues of ice on the White Continent and causes 10% of all the ice to flow out of the West Antarctic Ice Sheet into the ocean.

　　In recent years，satellite and airborne measurements have recorded a marked thinning of the PIG，which may be related to climate changes.But the team working on NASA’s IceBridge project said this latest birthing of a giant iceberg is part of a natural cycle seen every 10 years or so on the glacier.“The last big birthing event occurred in 2001 so，in general，people have been expecting something like this to happen fairly soon，and for us it is very exciting to see this while it is happening，”said IceBridge project scientist Dr Michael Studinger.

　　An iceberg of the size expected will need to be monitored carefully，not just because it could eventually become a danger to shipping.The biggest icebergs can have a major impact on their surroundings.As they break and melt，they pour millions of tons of freshwater into the local marine environment.Dust and rock fragments(碎片)picked up on land act as nutrients when they fall into the ocean，fuelling life right at the bottom of food webs.But these huge blocks can also put barriers in the way of animals trying to get to familiar feeding grounds.

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