What is logistics? In the current business environment,logistics is generally accepted as a very important element for the economic development and business growth of a region,especially a port city. In reality,what does logistics mean?In which way does it operate? For simple definition,logistics is a set of procedures in which commodity is delivered in an efficient manner from suppliers to customers.There are three key aspects to the concepts: 1．Movement of goods Goods can be considered as valuable objects,such as cargo and materials that are valua-ble and purchasable through commercial transactions and processes.Flow can be determined as methods in which goods are moved or transferred between locations,intermediaries and merchandisers.Modes of transportation include motor,rail,water,air and pipeline. 2.Direction of the flow of goods In the open market place,buyers and sellers represent two ends of a commercialtrans-action.Buyers are usually customers who demand the goods,while,as sellers are suppliers who provide such goods.When a transaction is agreed upon (sometimes payment is comple-ted,other times the payment is arranged to be completed at a later stage),the suppliers have the responsibility to arrange for the goods to be delivered to the customers. 3.Efficient management of the flow process The transportation of goods should bear low cost and ensure safety and punctuality.It should do its best to avoid wasting customers＇resources.Currently,the flow of goods is generally controlled by both hardware and software.By hardware,we mean logistics facili-ties and equipment,such as ports,warehouses and trucks,ships,railroad,cars and air-lines.By software,we mean information system,standardization and data sharing.Questions:

,Which of the following is a key aspect of logistics?( )

A:Goods. B:Customers. C:Suppliers. D:Movement of goods.

有3个作业J1、J2和J3，其运行时间分别是2、5和3小时，假定它们同时到达，并在同一台处理机上以单道方式运行，则平均周转时间最小的执行序列是( )。

A:J1，J2，J3 B:J3，J2，J1 C:J2，J1，J3 D:1).J1，J3，J2

作业J1，J2，J3，J4的提交时间和运行时间如表所示。若采用短作业优先调度算法，则作业调度优先次序为 (44) ，平均周转时间为 (45) (这里不考虑操作系统的开销)。