写出下面句子中横线上应该增译的内容。Last year, the output of coal in this region amounted to about 20 percent of the country, ____ of steel 25 percent, and ____ of cotton 35 percent. 去年, 这一地区的煤产量约占全国总产量的20%, 钢____占25%。棉花____占35%。