题目内容：

When an ice cube melts, it creates a puddle (水坑). When an ice sheet (冰盖)melts, it raises sea levels. It sounds simple, but scientists have debated for decades whether both the Antarctic and Greenland ice sheets actually were shrinking, and how much that melting contributed to rising sea levels.

Now, a new study has provided the best evidence of how the polar ice sheets are responding to our warming world. In the study, an international team of scientists looked at 20 years of' data in the ice sheets collected by 10 satellite missions. The team's conclusion: The Greenland and Antarctic ice sheets both are losing ice overall. The researchers also found that between 1992 and 2011, melt water from those shrinking ice sheets caused sea levels to rise by about 11 millimeters.

Over the 19 years studied, the Greenland ice sheet lost 2.7 trillion metric tons of ice. The  Antarctic ice sheet also shrank by about l.3 trillion metric tons. Previously, some scientists disagreed whether the Antarctic sheet, the largest mass of ice in the world, was shrinking or growing or neither.

While the Earth is warming overall, the effect of climate change varies from region to region. Over the last 15 years, for example, scientists have something disagreed over how climate change has affected the polar ice sheets. Many studies found that the sheets lost a lot of ice and that not enough snow fell on the sheets to compensate for the loss. But other studies found that the loss of ice was balanced by the gain in snowfall.

Richard Alley, a glacier scientist at Penn State University, said that many of those studies looked at different areas, and over different time periods. In addition, the studies didn't all use the satellite data in the same way. Those differences made, it difficult to compare the results.

The data in the new study matched time periods and areas. The study also combined measurements from kinds of satellites.

1.Why does the author use a common-sense phenomenon as the beginning?

A.To present the reason for ice sheet melting.

B.To show us the result of a scientific experiment.

C.To give a simple example to introduce the topic.

D.To present a common daily finding obvious to the readers.

2.The researchers reached their conclusion by_____.

A.analyzing the findings of former studies

B.observing the Antarctic and Greenland

C.referring to the data from satellites

D.making measurements in the Antarctic and Greenland

3.What does the underlined phrase "compensate for" in paragraph 4 refer to?

A.Cut down.

B.Lead to．

C.Bring about.

D.Make up for.

4.Which of the following might be the best conclusion for the passage?

A.Ice sheets are shrinking due to global warming.

B.People are suffering from climate change.

C.Rising sea levels makes people live in danger.

D.Shrinking ice has nothing to do with sea levels.