直流输电系统由哪几部分组成？是怎样工作的？
A branch office of Acme Insurance has 15 IP phones connected to the main office using the distributed call processing model. Normally， the phones work with great quality. However， during very busy times when all of the agents are on the phone at the same time， the voice quality drops precipitously. Words or phrases or both are dropped from conversations. What is the most likely cause of the problem？（） ["large files are being downloaded over the WAN network","IP phone traffic is not being classified correctly","more bandwidth is required for the office LAN","Call Admission Control has not been implemented ","employees are watching videos over the internet","header compression is not being used"]
低压配电系统的保护重复接地电阻不大于（）；接地装置的设计和施工应符合《工业与民用电力装置的接地设计规范》 ["4Ω；","10Ω；","20Ω；","1MΩ。"]
褶皱
假设伦敦国际金融期货权交易所的6个月期英镑合约交易单位为500000英镑。一家公司的财务经理以5%的利率借了100万英镑，期限为6个月。6个月后，贷款将会展期，这位财务经理担心那时利率会上升，所以决定卖出6个月的伦敦国际金融期货期权交易所的短期英镑期货，以对冲利率风险。请问：他需要卖出多少份合约？
《永乐大典》
