B :核酸的变性指核酸双螺旋区的氢键断裂,变成单链的无规则的线团,并不涉及共价键的断裂。一系列物化性质也随之发生改变:粘度降低,浮力密度升高等,同时改变二级结构,有时可以失去部分或全部生物活性。 DNA 变性后,由于双螺旋解体,碱基堆积已不存在,藏于螺旋内部的碱基暴露出来,这样就使得变性后的 DNA 对 260nm 紫外光的吸光率比变性前明显升高(增加),这种现象称为增色效应。因此判断只有 B 对。
【单选题】According to Unit 1 The Business of Language and the Language of Business , which statement is false ?
A.
Though the rules of genders in English are easier than those in some languages, its rules concerning grammar, spelling and pronunciation are much more irregular and difficult to follow.
B.
Germany and Japan were defeated by the English-speaking Americans and Englishmen because their prime ministers had some trouble in negotiating in English in 1940.
C.
Not only the French, but people from other countries such as Poland and Germany, feel the urgency of defending the encroachment of English.
D.
TV and radio, although being criticized for removing differences on a global scale, may in an opposite way extend the lifespan of some languages spoken by minority groups in small areas.