题目内容：

Directions: Read the following passage. Summarize the main idea and the main point(s) of the passage in no more than 60 words. Use your own words as far as possible.

Lower Oxygen Levels Threaten Marine Life

Oxygen in the oceans is being lost at an alarming rate, with “dead zones” expanding rapidly and hundreds more areas showing oxygen dangerously exhausted, putting sharks, tuna, marlin and other large fish species at particular risk. Dead zones, where oxygen is effectively absent, have quadrupled(翻两番) in extent in the last half-century, and there are also at least 700 areas where oxygen is at dangerously low levels, up from 45 when research was undertaken in the 1960s.

The reasons behind this environmental collapse are multiple. Among all, pollutants generated by the industrial world have been the most destructive force to cause the unbalance, including a rising tide of plastic waste, as well as other pollutants. Seas are about 26% more acidic than in pre-industrial times because of absorbing the excess carbon dioxide in the atmosphere, according to the Intergovernmental Panel on Climate Change, with damaging impacts on shellfish in particular.

Low oxygen levels are also associated with global heating, because the warmer water holds less oxygen and the heating causes stratification(分层), so there is less of the vital mixing of oxygen-rich and oxygen-poor layers. Oceans are expected to lose about 3-4% of their oxygen by the end of this century, but the impact will be much greater in the levels closest to the surface, where many species are concentrated, and in the mid to high latitudes.

Another major cause for lower oxygen is intensive farming. When excess artificial fertilizer from crops, or wastes from the meat industry, runs off the land and into rivers and seas, it feeds algae(藻类) which bloom and then cause oxygen consumption as they die and decay.

The problem of dead zones has been known about for decades, but little has been done to tackle it. Now is high time to take actions and help the oceans function better.