单项选择题

案例分析题Passage Two
Like many other industries, the telecoms industry is increasingly worried about its energy consumption and the associated carbon footprint. This is not just because rising energy prices have made it more expensive to run telecoms networks; it is also because telecoms networks and devices account for nearly 1% of global greenhouse-gas emissions, and the industry wants to avoid criticism from green advocates. Unlike many other firms, however, telecoms operators find their carbon footprints quite easy to work out. That is because their footprints are dominated by one thing: running their networks.
For example, Vodafone, a giant European mobile operator, estimates that its network accounts for 80% of its carbon footprint (the remainder is attributed to its offices, shops and vehicles). And three- quarters of the networks contribution is, in turn, associated with powering the base-stations that allow mobile phones to connect to the network.
Typically, around half of the operating expense of a network company goes on electricity. The proportion tends to be higher for operators in the developing world because their base-stations may be in remote areas, and therefore require diesel (柴油) fuelled generators. So the recent rise in energy prices has prompted operators to look for ways to cut costs.
Fortunately there are some relatively simple ways to reduce the energy consumption of a base-station. The first is to turn down the air-conditioning. Many mobile operators now run base-stations at a standard temperature of 35℃, rather than the previous norm of 25-30℃. Studies show that the higher temperature does not reduce the equipment’s reliability or life length. "The biggest limitation is actually our technicians, who do not like going into the hut to work at 35 degrees" says Andy MacLeod, Vodafone’s global networks director.
Operating at this temperature means ambient (周围的) air can be used for cooling, even in hot countries. An air filter is installed on one side of the cabin, and a fan is installed on the other, resulting in a steady flow of air. Vodafone plans to replace air-conditioning with this simpler approach, called "free cooling", in the majority of its base-stations over the next three years, as part of a plan to reduce its carbon footprint by 50% between 2006 and 2020.
According to Andy MacLeod, why was the base-station’s temperature set at 25-30℃ before