关于氟的抗龋机制，正确的描述是（） A.降低釉质的溶解性 B.促进釉质脱矿物质的再矿

Rising levels of carbon dioxide in the atmosphere are a major cause of climate change, and now a new study has confirmed that atmospheric CO2 is also affecting the ocean chemistry and potentially harming sea life.
Montana State University scientist Robert Dore has been researching the water in the Pacific Ocean for almost two decades.
"We've been going to the same spot in the Pacific Ocean, and we try and characterize long-term change in the open ocean environment. And one of the key things that we measure is CO2 levels. And we've been able to record this increasing quantity of atmospheric CO2 into the ocean."
Scientists expected that as atmospheric CO2 increased, more and more of the carbon dioxide would be absorbed into the ocean, affecting the chemical balance of the sea water, with a potentially harmful impact on shellfish and coral in particular.
"As carbon dioxide dissolves（溶解） in the water, or seawater in this case, it forms a weak acid, carbonic acid," Dore explains. "And therefore, as the concentration of CO2 in the atmosphere goes up and that exchanges with the surface seawater, it drives the pH down, and makes it more acidic."
The seawater Dore and his colleagues have analyzed confirms what the theory predicts.
The effect was particular striking at about 250 meters down, and again at 500 meters. Dore and his colleagues came up with two possible explanations. It could be that surface water picked up CO2 and then moved to those depths. Or there could be a biological explanation.
"It's important to realize that the oceans are really becoming acidic. And it can have negative impacts on a whole variety of sea life from fish to coral. It's potentially catastrophic."
53．What can be the best title of the passage?
A．Sea Life Facing Danger      B．Climate Change Affecting Seawater
C．Oceans Becoming More Acidic       D．Scientist Researching Seawater
54．Which of the following shows the process of the impact of atmospheric CO2 on sea life?
a．Sea life is endangered．
b．CO2 goes into the surface water．
c．The ocean chemistry is affected．
d．CO2decreases the PH and makes the seawater more acidic．
      e．CO2 levels in the atmosphere go up．

 
55．Scientist Robert Dore came to the conclusion based on__________.
A．his research and analysis
B．a major cause of climate change
C．some former theory
D．the expectation of other scientists
56．What does the passage want to tell us most?
A．It takes time to make a scientific study．
B．Atmospheric CO2 is doing harm to sea life．
C．Robert Dore is a committed and serious scientist．
D．Measures should be taken to prevent the potential catastrophe．