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问题 选择题

一次性使用的聚苯乙烯（）材料易造成“白色污染”，其替代物聚乳酸（）是由乳酸（）聚合而成的，聚乳酸可在乳酸菌的作用下降解。下列说法正确的是（  ）

A．聚苯乙烯的单体为

B．聚苯乙烯的聚乳酸的聚合方式相似

C．聚苯乙烯和聚乳酸均为纯净物

D．乳酸可发生消去反应

答案

答案：D

聚苯乙烯的单体为A项错误；合成聚苯乙烯的反应是加聚反应，聚乳酸是通过缩聚反应合成的，B项错误；由于n值不同，高分子化合物一般属于混合物，C项错误。

单项选择题

液压传动系统使用的液体主要是液压油，液压油除用来传递能量外，不包括下列（）作用。

A、润滑

B、冷却

C、密封

D、传质
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单项选择题

In the United States, the first day nursery was opened in 1854. Nurseries were established in various areas during the (91) half of the 19th century; most of (92) were charitable. Both in Europe and in the U. S. , the day-nursery movement received great (93) during the First World War, when (94) of manpower caused the industrial employment of unprecedented numbers of women. In some European countries nurseries were established (95) in munitions (军火)plants, under direct government sponsorship. (96) the number of nurseries in the U.S. also rose (97) , this rise was accomplished without government aid of any kind. During the years following the First World War, (98) , Federal, State, and local governments gradually began to exercise a measure of control (99) the day nurseries by (100) them and by inspecting and regulating the conditions within the nurseries.
The (101) of the Second World War was quickly followed by an increase in the number of day nurseries in almost all countries, as women were (102) called upon to replace men in the factories. On this (103) the U. S. government immediately came to the support of the nursery schools, (104) $6,000,000 in July, 1942, for a nursery school program for the children of working mothers. Many States and local communities (105) this Federal aid. By the end of the war, in August, 1945, more than 100,000 children were being cared (106) in day-care centers receiving Federal (107) Soon afterward, the Federal government (108) cut down its expenditures for this purpose and later (109) them, causing a sharp drop in the number of nursery schools in operation. However, the expectation that most employed mothers would leave their (110) at the end of the war was only partly fulfilled.

A．sources

B．abundance

C．shortage

D．reduction
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