4Dalsgaard, J.. P. T. , Lightofot, C. &Christensen, V. Towards quantifications of ecologicalSustainabilityinafrmingsystemsanalysis [ J ]. Eeol. Eng. , 1995 (4) : 181-189.
5Grossmna, S. J. The Information Role of Warrnaties and Private Disclosure About Porduct Quality[ J]. Journal of Lawnad Eeonomies, 1981 (24) :461-483.