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问题 单项选择题

缩合鞣质与酸作用的产物是

A．没食子酸

B．儿茶素

C．逆没食子酸

D．糖与没食子酸

E．鞣红

答案

参考答案：E

解析：缩合鞣质与空气接触，特别是在酶的影时下，很易氧化、脱水缩合为暗棕色或红棕色的鞣红沉淀。当有酸碱存在时速度更快。

单项选择题

An analyst conducts a two - tailed test to determine whether differences between the means of two populations exist: H0: μ1-μ2=0 versus H2: μ1-μ2≠0. Assume that the populations are independent, normally distributed, and have unequal and unknown variances. The critical value with 50 degrees of freedom is 2.126. The computed test statistic is t=1.753. Using a significance level of x=0.05, which of the following statements is TRUE（）

A. Use a t- test to reject the null hypothesis and accept the alternative hypothesis.

B. Use a t -test to accept the null hypothesis and reject the alternative hypothesis.

C. Use a z- test to reject the null hypothesis and accept the alternative hypothesis.
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单项选择题

以下（）不属于可以代维的工作内容。

A.问题整改

B.业主关系维系

C.工程建设

D.设备、设施周期监测
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