________（49）A.At three he knows about 1 000 words
________（49）
A.At three he knows about 1,000 words which he can put into sentences,and at four his language differs from that of his parents in style rather than grammar.
B.What was missing was good mothering.
C.Lots of information about benefits of baby signing and best ways to go about it can be found.
D.Insensitivity of the mother to these signals dulls the interaction because the child gets discouraged and sends out only the obvious signals.
E.If these sensitive periods are neglected,the ideal time for acquiring skills passes and they might never be learned so easily again.
F.And even more incredible is the young brain’s ability to pick out an order in language from the hubbub of sound around him,to analyze,to combine and recombine the parts of a language in novel ways.
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答案：F
该空前文提到人脑的特别之处，该空内容是该话题的延伸介绍。选项D 甚至更加不可思议的是，幼小的脑子能从周围的喧嚣声中听出语言表达的某种命令，用种种新奇的方式对某个语言的成分进行分析、组合以及重新组合，是对该话题的延伸介绍。所以，选项F是正确答案。