题目内容：

    Escaping predators (食肉动物), digestion and other animal activities—including those of humans—require oxygen. But that essential ingredient is no longer so easy for marine life to obtain, several new studies reveal.

In the past decade ocean oxygen levels have taken a dive—an alarming trend that is linked to climate change, says Andreas Oschlies, an oceanographer at the Helmholtz Center for Ocean Research in Germany, whose team tracks ocean oxygen levels worldwide. “We were surprised by the intensity of the changes we saw, how rapidly oxygen is going down in the ocean and how large the effects on marine ecosystems are,” he says. It is no surprise to scientists that warming oceans are losing oxygen, but the scale of the drop calls for urgent attention. Oxygen levels in some tropical (热带的) regions have dropped by an astonishing 40 percent in the last 50 years, some recent studies reveal. Levels have dropped less significantly elsewhere, with an average loss of 2 percent globally.

A warming ocean loses oxygen for two reasons: First, the warmer a liquid becomes, the less gas it can hold. That is why carbonated drinks go flat faster when left in the sun. Second, as polar sea ice melts, it forms a layer of water above colder, more salty sea waters. This process creates a sort of lid that can keep currents from mixing surface water down to deeper depths. And because all oxygen enters the surface, less mixing means less of it at depth.

Ocean animals large and small, however, respond to even slight changes in oxygen by seeking refuge in higher oxygen zones or by adjusting behavior, Oschlies and others in his field have found. These adjustments can expose animals to new predators or force them into food-scarce regions. Climate change already poses serious problems for marine life, such as ocean acidification, but deoxygenation is the most pressing issue facing sea animals today, Oschlies says. After all, he says, “they all have to breathe.”

Aside from food web problems, animals face various other physiological challenges as their bodies adjust to lower oxygen levels. Chinese shrimp (虾) move their tails less vigorously to preserve energy in lower oxygen environments. Some creatures, such as jellyfishes, are more tolerant of low oxygen than others are. But all animals will feel the impact of deoxygenation because they all have evolved their oxygen capacity for a reason, says Oschlies. “Any drop in oxygen is going to damage survivability and performance,” he says.

1.According to the first two paragraphs, what worries scientists the most?

A. The worsening deoxygenation in the warming ocean.

B. The survival of predators and various marine animals.

C. The alarmingly changeable oxygen levels in the ocean.

D. The lack of attention to the warming of tropical oceans.

2.Which of the following is a reason for the oxygen loss in the ocean?

A. Polar ice melting consumes much oxygen in the ocean.

B. Global warming reduces the amount of oxygen in the air.

C. The surface polar ice water prevents oxygen going down.

D. Salty water holds less gas in the increasingly warmer ocean.

3.What can be inferred from the passage?

A. Ocean deoxygenation changes some animals’ natural territories.

B. Ocean acidification is more serious a problem than deoxygenation.

C. Not all ocean animals are bothered by the decreasing oxygen levels.

D. Some animals reduce their movements in order to absorb more oxygen.

4.Which of the following is the best title of the passage?

A. The Oxygen Levels of Marine Life B. Ocean Warming Affects Food Web

C. The Survivability of Ocean Animals D. The Ocean Is Running Out of Breath