Two pressing problems face the world: economic meltdown and global warming. Conveniently, a solution presents itself that apparently solves both: governments should invest heavily in green technology, thus boosting demand while transforming the energy business. This notion is gaining agreement around the world. Last month the United Nations called for a "Global Green New Deal". But it is in America that the idea is really taking off. The United States Conference of Mayors reckons that green investment should provide 2.5m jobs. The Centre for American Progress thinks $100 billion worth of spending in the area would provide 2m jobs. The new president tops both. Barack Obama proposes spending $150 billion over ten years, thus helping, he says, to create 5m jobs. There is a historical parallel to this synergy between two worthy aims. Just as military spending at the end of the 1930s defeated both fascism and the Depression, so spending on fighting climate change should both wean (使摆脱) mankind off fossil fuels and avert what might otherwise turn into the most serious downturn (衰退) since the 1930s. Isn’t that neat But combining the two by subsidizing renewable energy is, like many easy answers, the wrong solution. Governments can discourage companies and people from producing CO2 by making polluters pay or by reducing the costs of clean energy. Europe does both, through a cap-and-trade system (which caps CO2 emissions and requires companies to buy permits to pollute) and through subsidies. Mr. Obama is, quite rightly, planning to introduce a cap-and-trade system, but he is also promising massive subsidies. Subsidies are more popular but both theory and practice argue against them. Subsidizing clean energy requires politicians to decide on the best way of delivering it, and their judgment is likely to be worse than the market’s. America’s huge ethanol (乙醇) subsidies, for instance, have led to overinvestment in the businesses, which is now experiencing a sharp crash, and have helped drive up the price of food, with painful consequences for the world’s poor. The easy notion that there is a single solution to the world’s economic and climatic problems is, thus, a dangerous one. The world needs America to lead the fight against climate change. But if Mr. Obama goes about it the easy way, rather than the right way, he will discredit the cause he advocates, and thus damage the planet instead of saving it. The word "synergy" (Line 1, Para 2) most probably means______.

A. cooperative interaction
B. discord of action
C. disagreement of opinion
D. diversity of idea