|  c is no problem. 
 (However, original context ‘…even though no new mines have opened..’, i think, is inappropriate     because, if there are more  
 new mines, mine companies need to hire more workers even with advanced machines, then output per miner could be constant or even lower.) 
 Therefore, i agree what a mm above said ' 
 A是个比较隐蔽的答案,arundhati,你有没有发现,conlusion的难题都是用一些抽象的词或是概括的话去代替原文中的名词......我想是老美可能就不存在这种障碍了。这题也是同样的,工人数不变就是没有开新矿的代名词。' |