阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项。

How often do you travel by plane？

　　How much electricity do you use? These days everyone is worried about the size of their carbon footprint．In order to reduce global warming we need to make our carbon footprints smaller．But how much CO₂ are we responsible for?

　　A new book by Mike Berners Lee(a leading expert in carbon footprint)might be able to help．How Bad are Bananas? The Carbon Footprint of Everything looks at the different things we do and buy, and calculates the amount of CO₂ all of the following created：the ingredients, the electricity used in the brewery, the equipment, the travel and commuting of the beer, and the packaging．It’s amazing how many different things need to be included in each calculation．And it’s frightening how much carbon dioxide everything produces．

　　But all of this can help us decide which beer to drink．From Berners-Lee’s calculations, it’s clear that a pint(568ml)of locally-brewed beer has a smaller carbon footprint than a bottle of imported beer．This is because the imported beer has been transported from far away, and it uses more packaging．The local beer only produces 300g of CO₂, but the imported beer produces 900g! So, one pint of local beer is better for the environment than three cans of cheap foreign lager from the supermarket．

　　Berners-Lee has even calculated the carbon footprint of cycling to work．Nothing is more environmentally-friendly than riding a bike, surely? Well, it depends on what you’ve had to eat before．To ride a bike we need energy and for energy we need food．So if we eat a banana and then ride a kilometer and a half, our footprint is 65g of CO₂．However, if we eat bacon before the bike ride, it’s 200g．In fact, bananas are good in general because they don’t need packaging, they can be transported by boat and they grow in natural sunlight．

　　So, does this mean that cycling is bad for the environment? Absolutely not, for a start, if you cycle, you don’t use your car, and the fewer cars on the road, the fewer traffic jams．And cars in traffic jams produce three times more CO₂ than cars traveling at speed．Cycling also makes you healthy and less likely to go to a hospital．And hospitals have very big carbon footprints!

　　So maybe it’s time for us all to start making some changes．Pass me a banana and a pint of local beer, please．

阅读理解

　　Scientists have long understood the key role that oceans play in regulating the Earth's climate．Oceans cover 70 percent of the globe and store a thousand times more heat than the atmosphere does．What's newer is the understanding of how this key component(组成)of our climate system responds to global warming．

A brake on global warming－for now

　　One of the ocean's most important climate functions is absorbing heat and carbon dioxide(CO₂), one of the gases that cause global warming．Acting as a heat sponge(海绵), the oceans have absorbed huge amounts of heat and CO₂ in the last forty years．

　　Fujita explains that “the oceans are saving us from faster climate change－they are a big flywheel that delays rapid overheating of the earth, putting a brake on the climate system．”

　　“That's the good news,” he adds．“The bad news is that the oceans only slow the atmospheric warming．Once the oceans come to balance with a greenhouse-gas warmed earth, the extreme heat will remain in the atmosphere and things will get much hotter．” But where and how the oceans release this accumulated(积累)heat is uncertain．And as the ocean stores heat, fragile(脆弱的)underwater ecosystems are struggling．

　　The most recent scientific report from the Intergovernmental Panel on Climate Change(IPCC)also　notes with concern that the ocean is acidifying(酸化)because of increased absorption of atmospheric CO₂, and thus causing a threat for shell-forming species．Sharp increases in carbon dioxide levels will cause further acidification of the ocean．

Currents distributing heat

　　Another important role the oceans play is that of distributor．Oceans deliver heat and life-sustaining nutrients around the globe．Just as blood vessels bring oxygen and nutrients to cells in the human body, the ocean's currents carry oxygen, nutrients and heat throughout the Earth．The ocean distributes 25 to 50 percent of the energy the planet receives from the sun．For example, the Gulf Stream carries heat across the Atlantic．This warm current gives northwestern Europe a milder climate than it would normally have so far north．A change to the ocean's circulation(循环)patterns could throw Europe into a colder period, even as the rest of world experiences warmer temperatures．