Text 3 Transporting large containers is not as glamorous as making films, but shipping is doing more than Hollywood to boost southern California's economy these days. The nearby ports of Los Angeles and Long Beach, already the two biggest in the country, are growing quickly thanks to trade with China. They are a giant job-creating engine, stimulating industrial and warehouse employment on a scale not seen in the region since the rise of the aerospace industry after the Second World War. Sadly, like most engines, they are filthy.

The ports themselves reckon they are responsible for about 12% of all the diesel particle emissions and 45% of the sulphur oxides (硫的 氧化物) in southern California. Carried east by prevailing winds, such pollutants help to create some of America's worst air more than 50 miles inland. Those who live close to the freeways leading out of the ports suffer the most. Researchers have found that children living within a few hundred meters of such roads are not only more likely to suffer from asthma, a disease of the breathing system and characterized by sudden recurring attacks of labored breathing, and coughing. They actually have smaller lungs.

The most ambitious effort to control pollution, and the one that may affect the local economy most drastically, involves truckers. Some 16,000 lorries currently haul containers between ships and warehouses, most of whom are owned by Hispanic immigrants. The drivers put in long hours: 13 a day is not unusual, according to a survey. They earn, on average, just under $35,000 a year. Such jobs, like many connected to the port, are an important stepping-stone on the path to the middle class.

The ports want to remove the oldest trucks and gradually upgrade the others so that, within five years, the fleet emits four-fifths less pollution than at present. To help pay for this, they intend to levy (征收-) a fee of $34 to $54 on every “dirty” vehicle entering the port. Most important, they want to turn a large, unwieldy network of independent contractors into a more orderly group of companies, as happens in an airport. “We need to have more control,” explains Geraldine Knatz, the head of Los Angeles' port.

The reforms do nonetheless pose a threat to the ports' competitiveness. At present, the truckers who work at the docks are price-takers, not price-setters. Because they are self-employed, they are almost impossible to unionize, and consequently have little bargaining power. All that could quite easily change if they were to become the employees of a few large firms. Indeed, the most enthusiastic welcome for the ports' plans has come not from environmental groups but from the Teamsters' union.

第31题：What is the passage mainly about?

［A］The consequences of shipping industry in southern California.

［B］The causes of pollution along the coast of southern California.

［C］The pollution problem of the shipping industry in southern California.

［D］The role of shipping industry in southern California's economy.