填空Climate change is one of the most fundamental challenges ever to confront humanity. Its impacts are already showing and will intensify over time ___1___ left unchecked. There is overwhelming scientific evidence, ___2___ shown in the Fourth Assessment Report (第四次评估报告的综合报告 ) of the Intergovernmental Panel on Climate Change (IPCC) (政府间气候变化专门委员会), that climate change will threaten ___3___ growth and long-term prosperity, as well as the very survival of the most vulnerable populations. IPCC projections indicate that if emissions continue to rise at their current ___4___ and are allowed to double from their pre-industrial level, the world will face an average temperature ___5___ of around 3℃this century. Serious impacts are associated ___6___ this scenario (情景), including sea-level rise, shifts in growing seasons, and an ___7___ frequency and intensity of extreme weather events such as storms, floods and droughts. The United Nations Climate Change Conference in Copenhagen in December in 2009 offers a ___8___ opportunity to step up international action on climate change. A Copenhagen deal is ___9___ the global transition into green economic growth, and, most urgently, to help the world, especially the most vulnerable, to adapt to impacts ___10___ are now inevitable. 1.A. if B. whether C. when D. which 2.A. because B. as C. while D. when 3.A. economics B. economical C. economy D. economic 4.A. speed B. rate C. pace D. rhythm 5.A. rising B. rise C. raise D. raising 6.A. with B. to C. from D. in 7.A. being increased B. increased C. increase D. increasing 8.A. history B. historical C. historic D. historically 9.A. necessary B. inevitable C. essential to D. basic 10.A. that B. of which C. who D. what