studentscanfindeverythingtheyneedtolookupwhendoingresearchpaperorreadingforfun句子中的doing和reading是动名词还是分词?如果是分词,为什么要这么用?不能是doresearchorreadforfun

　　studentscanfindeverythingtheyneedtolookupwhendoingresearchpaperorreadingforfun

　　句子中的doing和reading是动名词还是分词?如果是分词,为什么要这么用?不能是doresearchorreadforfun