微型机的DOS系统属于哪一类操作系统A．单用户操作系统 B．分时操作系统 C．批处理

俯视图和左视图中相应投影高度相等。

请结合图示实验装置，回答下列问题。

（1）图中a、b仪器的名称：a    ，b    。

（2）用高锰酸钾固体制氧气，选用的发生装置是    （填“A”、“B”或“C”），装入药品前应先进行的操作是    ，反应的化学方程式是    。

（3）某同学在实验室用C装置（多孔隔板用来放块状固体）制取CO₂，反应的化学方程式为    ， C装置与B装置相比较，优点为    （答出一点即）。

（4）实验室用B装置制取H₂时，b中应加入    。如要获得干燥的气体，除发生装置外，还应选用盛放    （填写试剂名称）的D装置。如用E装置收集H₂，则气体应从    端通入（填“c”或“d”）。

某企业上年度销售收入为20000元，本年度销售收入为80000元。按照资金习性分析，每1元销售收入所需变动资金为0.30元。则该企业本年度新增的资金需要量为( )元。

A．6000

B．12000

C．18000

D．24000

下列关于静态投资评价指标的有关讨论中，不正确的是( )。

A．投资收益率没有考虑投资收益的时间因素，指标的计算主观随意性太强

B．静态投资回收期是在不考虑资金时间价值的条件下，以项目的净收益回收其全部投资所需要的时间

C．资本周转速度愈快，回收期愈短，风险愈小，盈利愈多

D．根据偿债备付率的计算公式，偿债备付率必须按年计算

Beijing: The United States and North Korea had their first ______ in four months here this afternoon as part of the ______ negotiations on how to end North Korea’s nuclear program, but diplomats played down prospects for______. James A. Kelly, assistant ______, and Kim Yong Ⅱ, North Korea’s deputy foreign minister, met ______ of formal discussions, ______ on direct dialogue that began after a stormy meeting ______ in which North Korea warned that it was moving quickly to ______ nuclear arms. The Bush administration had insisted ______ that it would only hold talks with North Korea ______ because, it argued, only ______ pressure would persuade North Korea to______. It got its way when North Korea dropped its insistence on ______ and agreed, after extensive efforts by China, to hold unusual simultaneous negotiations with ______,______,______ and ______ as well as the United States. Though Bush administration officials had not ______ talking privately with the North Koreans during______, the fact that Mr. Kelly and Mr. Kim met on the first day was seen as a sign of ______ by the American side.