介词后面的现在分词是宾语还是状语?如何区别?例如,asayoungman,hesawthegreatneedforincreasingthericeoutput.(答案是increasing做宾语)YuanLongpingsearchedforawaytoincreasriceharvestswithoutexpandingtheare

　　介词后面的现在分词是宾语还是状语?如何区别?例如,

　　asayoungman,hesawthegreatneedforincreasingthericeoutput.(答案是increasing做宾语)

　　YuanLongpingsearchedforawaytoincreasriceharvestswithoutexpandingtheareaofthefields.(答案是expanding做状语)

　　请解释这两题答案的理由,并分析介词后面的现在分词是宾语还是状语,区别的标准.