分类法是化学学习和研究的重要方法之一。下列分类正确的是【】

【名词&注释】

历史数据(historical data)、混合物(mixture)、硫酸铝(aluminum sulfate)、分类法(classification)、小苏打(sodium bicarbonate)、算术平均数(arithmetic mean)、非金属元素(nonmetal elements)

[单选题]分类法是化学学习和研究的重要方法之一。下列分类正确的是【】

A. 非金属元素^{(nonmetal elements)}：Mg、F、Si
B. 盐：纯碱、小苏打、硫酸铝
C. 混合物：空气、石油、冰水共存物
D. 合成材料：塑料、羊毛、合金

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学习资料：

[单选题]（ ）是预测将来某一时期的平均预测值的一种方法。该方法按对过去若干历史数据求算术平均数^{(arithmetic mean)}，并把该数据作为以后时期的预测值。

A. 简单移动平均法
B. 指数平滑法
C. 趋势外推法
D. 因果分析法

[单选题]Dear Linda，I’ve got a problem and as．l don't know what to do，l think I'd write to you and ask for your advice．I have worked at a (11) factory for about two months till now．It's a part-time job，so I only work in the evening．I've recently (12) that one of my workmates is stealing． From time to time，l notice that he puts a piece of meat under his trousers just (13) he leaves the facto- ry． Now the manager has found that things are (14) ． But he says that all this (15) after I started working．What should I do? Maybe I (16) tell that workmate I knew (17) he was doing． Or possibly I should go to the manager and tell him who was (18)meat．I think I-m in a(n) (19) position. Please tell me how I can solve this problem．I'd like to have your (20) ．Best wishes，

A. Yours，
B. Carl
D. fruit
E. metal
F. tomato
G. meat

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