Polar bears live mostly on ________ sea ice, which they use as _______ platform for hunting seals. A. a; a B. a; the C. 不填; a D. the; 不填 答案:C解析: ice 是不可数名词,在这里是泛指。不可数名词即使前面有半泛指性定语也不加the. 如:Chinese history; platform 是可数名词, 用a表示泛指3.一项工程,甲独做要4天完成,乙独做要5天完成,甲乙的工效比是5:4,甲的工效比乙快25%.