乳酸在一定条件下所形成的聚酯的结构简式为，该酯可以作为新型的_爱下问搜题

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问题选择题

乳酸在一定条件下所形成的聚酯的结构简式为，该酯可以作为新型的餐具原料。由它所产生的塑料在乳酸菌作用下，能迅速分解为无毒物质，可以降解。下列有关这种新型的可降解塑料的叙述正确的是（　　）

A．降解塑料是一种纯净物

B．其生产过程中的聚合方式与聚苯乙烯相似

C．它属于一种线型高分子材料

D．其相对分子质量为72

答案

C

该降解塑料是乳酸在一定条件下的聚合产物，其聚合度n值是不确定的，它是相对分子质量大小不等的混合物，A项错。由乳酸生成其聚酯属于缩聚反应，它的链节彼此连接在一起形成一条长链，属于一种线型高分子化合物，而苯乙烯生成聚苯乙烯发生的则是加聚反应，故B项错。塑料都有热塑性，故其属于线型高分子材料，C项正确，该聚合物的相对分子质量为72n，D项错，故应选C项。

完形填空

As Christmas is coming，there are presents to be bought，cards to be sent，and rooms to be cleaned．Parents are 36 with difficult jobs of hiding presents from curious young children·If the gifts are large，this is sometimes a real   37 On Christmas Eve， young children find the excitement almost unbearable They are torn between the wish to go to bed early so that Father Christmas will bring their presents quickly and the wish to 38 up late SO that they will no’ 39 the fun．The wish for gifts usually proves stronger．But though children go to bed early， they often lie   40 for a long time，hoping to get a short 41 at Father Christmas．
Last Christmas，my wife and I 42 hid a few large presents in the storeroom．I feared the   43 when my son，Jimmy，would 44 me where that new bike had come from，but 45 he did not see it．
On Christmas Eve, 46  took the children hours to go to sleep．It must have been nearly   47 when my wife and 1 went quietly into their room and began    48 stockings(袜子) ．Then I pushed in the 49   I bought for Jimmy and left it beside the Christmas tree．We knew we would not get much sleep that night，for the children were 50 to get up early At about five o’clock the next morning， we were 51  by loud sounds coming from the children’s room--they were shouting excitedly! 52 I had time to get Out of bed，young Jimmy came riding into the room on his new bike，and his sister，Mary，followed close behind pushing her new baby carriage． 53 the youngest baby arrived He moved 54 the hands and knees into the room dragging a large balloon behind him Suddenly it burst．That woke us up 55 ．
The day had really begun with a bang(巨响)!

D．successfully

D．fortunately

小题15:A．afraid B sure C．surprised D．excited

小题18:A．Even B But C．So D．Ever

填空题

组合框和列表框的主要区别是：是否可以在框中【9】。