The dark depths of the oceans are often called Earth's final frontier，but one researcher says the dirt beneath our feet is just as mysterious."We know more about the surface of Mars than we do about either oceans or soils on Earth，" says Mare Kramer，who thinks getting more dirt on dirt could produce some huge benefits for the entire planet.
   In a study published in November，Kramer，an assistant professor of environmental chemistry at Washington State University Vancouver，digs deep into what scientists know about how soil stores carbon，and explores some strategies for pulling carbon dioxide from the atmosphere.Researchers know carbon dioxide can be absorbed by tees，soil microorganisms and crops.Kramer's study shows that it can also be stored in soil minerals over a foot beneath the surface.
   The research Kramer and other scientists have been building upon could help them tailor farming and other practices to get carbon out of the atmosphere.In Kramer's earlier study in 2015，farmers were able to raise the carbon levels in their soil to that of native forest soils in just six years.
   Having dirt clean the air is an appealing paradox （矛盾現(xiàn)象），but some scientists are throwing mud on that pattern.Researchers at the University of California，Irvine，found the soil's ability to absorb carbon was wildly overestimated.Another warning：Soil，though it can store carbon，has also been found to release carbon dioxide as its temperature rises.In the 1990s，scientists heated the ground of forest plots by several degrees and found that the carbon released from the soil increased greatly.
   Kramer notes that the long range study looked at the top layer of soil，which interacts with the atmosphere more readily，while his most recent study dealt with soils at least I foot beneath the ground.The minerals in that layer allow it to hold on to carbon more persistently.
   In June，the United Nations said the world population is expected to reach 9.8 billion by 2050.Increasing our knowledge of soil will help farmers grow more crops effectively，improve water retention（保留） in the soil and keep carbon in the soil，Kramer says.

（1）What do Marc Kramer's words in Paragraph 1 suggest？

D

D

A．Mars is still a mystery to us.
B．Exploring Mars is of great significance.
C．We actually know little about the soil on Earth.
D．Oceans and soils on Earth are equally important.
（2）How do researchers at the University of California look at Kramer's study？

D

D

A．They couldn't agree more.
B．They think the finding is convincing.
C．They think more research should be done.
D．They have different opinions from Kramer's.
（3）What makes his latest study different from previous studies according to Kramer？

B

B

A．The research method.
B．The targeted depth of soil.
C．The way he stores carbon.
D．The theory behind the research.
（4）Which of the following may Kramer agree with？

C

C

A．We can't raise the carbon levels in the soil.
B．The top layer of soil can hold carbon persistently.
C．A better knowledge of soil may increase food production.
D．Warm temperatures may cause soil to release more carbon.