题目

Foreach blank in the following passage there are four words or phrases marked A,B, C and D. Fill in each blank with the word of phrase that best fits thecontext. From the nation's earliest days, farminghas held a crucial place in the American economy and culture. Farmers play animportant role in any society, of course, since they feed people. But farminghas been particularly 1 in the United States with intensifiedattention from civilians and government as well. Early in the nation's life, farmers wereseen as exemplifying economic 2 such as hard work, perseverance, andself-sufficiency. Moreover科学家发现，随着大气层中的悬浮物质和其它微粒增加，近几十年以来，到达地球的太阳辐射量减少了10%，地球正在“变暗”．与“变暗”有关的大气热力作用是（　　） A、①B、②C、③D、④