假定某服务的参考流是1000吨钢材，已知吨钢能耗750kgce，则每功能单位(Function Unit)在材料生产阶段的能耗是（ ）Assuming that the reference flow of a service is 1000 tons of steel and that the energy consumption of one ton of steel is 750 kgces, the energy consumption per functional unit of (function unit) in the material production phase is （ ）