试述L型细菌及其形成机理和培养特点。
参考答案：
L型细菌，即细菌细胞壁缺陷的细菌，因其首先由李斯特(Lister)研究院所发现，故取其第一个字母而称之。细菌细胞壁的主要成分是肽聚糖，由于作用于细胞壁的抗生素、溶菌酶等因素的影响，当肽聚糖结构遭受破坏或其合成受到抑制时。虽然大多数细菌裂解死亡，但有时也有一些细菌不死，这些细菌即L型菌。L型菌需在高渗低琼脂(0．8％～0．9％)的含血清(20％)培养基中培养，生长缓慢，一般生长期为2～7天，菌落为"油煎蛋，状，需放大100倍左右才能看到菌落，可通过传代培养而返祖。
| 完形填空。 阅读下面短文,掌握其大意,然后从A、B、C、D四个选项中选出可以填入空白处的最佳选项。 | |||
| There was a blind girl who hated herself because she was blind. In fact, she 21 nobody except her boyfriend,for he was always 22 to help her. She used to tell her boyfriend,"If I could see the 23 , I would marry you. '' One day, someone donated(捐赠) a pair of 24 to her. When the bandages(绷带) came off, she was able to see everything , including her boyfriend, for the 25 time. He asked her,"Now that you can see the world,will you 26 me?" The girl looked at her boyfriend and was greatly surprised to see that he was 27 . She had never expected that. She would not like to be with a blind husband for the rest of her life , so she 28 to marry him. Her boyfriend left in tears and a few days later wrote a 29 to her, saying,"My dear,take good careof your eyes. 30 they are yours, they were mine. " This is how the human brain (人脑)often works when our status (地位)changes. Only a very few remember what 31 was like before. And we often ask for more than we need. Life is a gift. Today,before you complain about the 32 of your food , think of someone who has nothing to 33 . Before you complain about life, think of someone who went to heaven(天堂)too early. Before you complain about your old 34 , think of the people who are living in the streets. And when you are tired and complain about your job , think of those who have no jobs. So 35 what you have and don't forget your past. | |||
| ( ) 1. A. forgot ( ) 2. A. ready ( ) 3. A. Sight ( ) 4. A. shoes ( ) 5. A. first ( ) 6. A. follow ( ) 7. A. ugly ( ) 8. A. decided ( ) 9. A. diary ( ) 10. A. Before ( ) 11. A. mind ( ) 12. A. taste ( ) 13. A. do ( ) 14. A. food ( ) 15. A. forget | B. loved B. unhappy B. world B. glasses B. second B. love B. sick B. agreed B. note B. After B. work B. size B. wear B. house B. spend | C. disliked C. angry C. earth C. trousers C. next C. marry C. short C. refused C. song C. Once C. school C. color C. eat C. clothes C. enjoy | D. thanked D. sad D. people D. eyes D. last D. see D. blind D. wanted D. story D. Since D. life D. shape D. make D. bus D. pay |