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草坪草的一般特性有哪些？

答案

参考答案：

草坪草的一般特性有以下几点：

（1）耐践踏性强

（2）耐修剪

（3）叶片多数，一般小型、细长、直立。使草坪具一定弹性。

（4）多为低矮的丛生型或匍匐茎型，覆盖力强，能形成地毯状草皮

（5）适应性强，生长旺盛，分布广泛，再生能力强，损伤后能迅速恢复。

（6）结实率高，容易收获，发芽性强；或匍匐茎发达，能强而迅速地向周围空间扩展，因而易于建成大面积草坪。

（7）无刺无毒，无不良气味，叶汁不易挤出

单项选择题

An analyst does research about expected return and expect standard deviation of return from investment portfolio. Two assets have the same expected return and the same expected standard deviation of returns. The correlation coefficient of returns between the two assets is expected to be +0.6. Which of the following statements best describes the standard deviation of a portfolio composed of those two assets
If the two assets are combined to form a portfolio, the expected standard deviation of that portfolio will be:（）

A. the same as the expected standard deviation of returns for each asset because the correlation coefficient of returns is positive.

B. less than the expected standard deviation of returns for each asset because the correlation coefficient of returns is less than +1.0.

C. unaffected by the portfolio weights used for each of the two assets because the assets have the same expected return and the same expected standard deviation of returns.
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单项选择题

从经济的角度看，明清时期中国已处于“近代的前夜”。下面能够说明这一结论的是（）

A.租佃制经营方式的推广

B.制瓷、矿冶等手工业技术均有较大进步

C.苏州丝织业“小户”“听大户呼织”，“计日受值”

D.世界白银的一半流入中国，市面上大量使用白银
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