什么叫氮源？试从分子水平和培养基原料水平列出微生物的氮源谱。
Given that Thing is a class， how many objects and reference variables are created by the following code？（） Thing item， stuff； item = new Thing（）； Thing entity = new Thing（）； ["One object is created","Two objects are created","Three objects are created","One reference variable is created","Two reference variables are created","Three reference variables are created."]
养老保险经办机构能否协助法院将离退休人员养老金抵偿债务（） ["可以协助法院查封退休人员的养老金帐户","可以协助法院冻结退休人员的养老金帐户","可以协助法院将退休人员养老金直接划入法院","不能直接扣发退休人员养老金抵偿债务"]
遥感平台
简述《幼儿园教育指导纲要》（试行）对幼儿社会领域教育总目标的规定。
如果流量计算机故障，在更换新的流量计算机后，应该注意哪些事项？
