单项选择题The ______ feature is considered central to human language, which means two levels of structure or patterning .
单项选择题The tone of this text is ______.
单项选择题According to the text the newsagent last wrote out Topham’on the top right-handed comer of the author's paper because ______.
单项选择题The research reviewed in the passage suggest that ______.
单项选择题Helsing speculates that husbands suffer from the death of a spouse because they are ______.