某企业“生产成本”账户的期初余额为48500元，本月借方发生额为60000元，期末生

简述不当得利的概念及构成要件。

按要求填写化学符号或名称：

氦气______；  2个氢分子______；   2个镁离子______；

硫离子______；  氯离子______；   氯酸钾______；

碳酸钠______；  硫酸______；硝酸铵中氮的化合价______；

K₂MnO₄______； Ba（NO₃）₂______； Fe（OH）₂______．

(2011·福建龙岩)如图所示，a、b、c、d四个图是不同的单色光形成的双缝干涉或单缝衍射图样．分析各图样的特点可以得出的正确结论是                  (　　)

A．a、b是光的干涉图样

B．c、d是光的干涉图样

C．形成a图样的光的波长比形成b图样光的波长短

D．形成c图样的光的波长比形成d图样光的波长短

( )科目编码必须按财政部的统一编码方案进行编制。

A．明细

B．末级

C．一级

D．二级

When a risk-free asset is combined with a portfolio of risky assets, which of the following is least accurate（）

A. The standard deviation of the return for the newly created portfolio is the standard deviation of the returns of the risky asset portfolio multiplied by its portfolio weight.

B. All risk-return combinations between the risk-free asset and the risky asset portfolio can be represented by a straight line that connects the point in the risk-return plane representing the risk-free asset, with the point representing the risky asset portfolio.

C. The variance of the resulting portfolio is a weighted average of the returns variances of the risk-free asset and of the portfolio of risky assets.