问题
单项选择题
与成熟B细胞比较，活化B细胞表面何种免疫球蛋白逐渐消失（）
A.IgA
B.IgD
C.IgE
D.IgG
E.IgM
答案
参考答案：B
解析：IgD是B细胞分化成熟的标志，未成熟的B细胞仅表达mlgM，成熟B细胞同时表达mlgM和mlgD，活化后B细胞和记忆B细胞上的mlgD消失。
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与成熟B细胞比较，活化B细胞表面何种免疫球蛋白逐渐消失（）
A.IgA
B.IgD
C.IgE
D.IgG
E.IgM
参考答案：B
解析：IgD是B细胞分化成熟的标志，未成熟的B细胞仅表达mlgM，成熟B细胞同时表达mlgM和mlgD，活化后B细胞和记忆B细胞上的mlgD消失。
People from Great Britain brought the English language to North America in the 16th and 17th centuries. And in the __36__ 300 years, there were so many___37__ in both places that now people can easily___38__ an English person from an American in the___39__ he or she talks. Many old words___40__ in England but were kept in America．For example,300 years ago people in Great Britain got their water from something they__41__either a“faucet”,“spigot”,or a“tap”.All these words are___42__ heard in different parts of America, but only “tap”is still___43_ in England．Americans often make___44__ new words or change old ones. “Corn”is one kind of plant in America and__45__ in England． Also, over the last three centuries the English language has___46__ thousands of new words for things that weren’t___47__ before. And often, American and Eng  lish people used two__48__ names for them. A tin can is called“tin”for short in English, but a “can”in America．The word “radio”is__49__all over the world, including America．But many English people call it a “wireless”.And almost anything___50__ something to do with cars, railroads, etc．has different___51__ in British and American English.But now American and British English may be___52__ closer together. One thing is that__ 53_ people can hear a large amount of American speech daily in___54__, on television, or from travelers. Because of this, Americans___55__ to be influencing the British more and more. So some day, English may even be the same on both sides of the Atlantic．
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