Yet, facing with so many contToversia1 experimeni materials (Da1ton,1993; Smith, 1986; MUrnane & Phelps, 1995: Dougal & Caren, l999), themodel needed further developmeni in order to explain more exactly.

• 然而，面对它们各自所持有的实证依据（Smith，1986；Dation，1993；Murnane & Phelps，1995；Dougal & Caren，1999），一般场合模型的解释力还是很有限的，其中仍有许多潜在的变量和机制亟待发掘和探测。