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当空气中二氧化碳浓度超过时会使人失去知觉，甚至死亡。

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在基因表达的调控系统中，在调节蛋白不存在时，基因是表达的；加入某种调节蛋白后，基因的表达被关闭，这样的调控机制和调节蛋白称为( )。

A. 负调控、诱导蛋白
B. 正调控、诱导蛋白
C. 负调控、阻遏蛋白
D. 正调控、阻遏蛋白

诱导系统中的阻遏物是（）：

A. 组蛋白
B. 含有较多的RNA，因而能使其识别特异的操纵基因
C. 直接结合到DNA的特异区域
D. 是由与结构基因相邻的操纵基因编码的

根据雅各布和莫诺的乳糖操纵子模型，结构基因的表达受控于一个开关单位，这个开关单位称为，而这个开关单位是否开放又受到的控制。

U102 Summary of Text AComplete the following passage with words chosen from this unit. The initial letter of each is given.Many of us these days are learning a foreign language. We are interested in learning another language because we know that knowledge of another language and culture will increase our career opportunities, broaden our horizons and enrich our life. Since learning a foreign language is of such importance, no 1) d people are constantly looking for more 2) e ways of language learning. Most people say the best way to learn a language is to stay in the country where it is spoken. It is true those who go to a native country have an 3) a over those who don't. But living abroad needs money, and not everyone can 4) a to do so. Those who don't go abroad may turn to language schools for help. Language schools usually 5) c that they can teach students to speak the language they want to learn 6) f within 3 to 6 months because they have more 7) q teachers and better facilities, but it would be 8) r to claim that any teacher has discovered a perfect way of teaching English in every possible situation. In fact, there are 9) a many good methods of teaching a language as there are good teachers, because every teacher is an 10) i____ with his / her own personality. What a student needs to remember then is to find out a method that best suits himself / herself.