5Halliday M,Hasan R.Cohesion in English[M].London:Longman Group Limited,1976:4-6.
6Van Dijk,T.A.Text and Context:Explorations in the Pragmatics of Discourse[M].London:Longman,1977:93.
7Beaugrande,R.D.Introduction to Text Linguistics[M].New York:Longman Group Limited,1980:84.
8Brown,C.Topic Continuity in Written English Narrative[C]// T.Givón.Topic Continuity in Discourse.Philadelphia:John Benjamins Publishing Company,1983:320-323.
9Davison,Alice.Syntactic Markedness and the Definition of Sentence Topic[J].Language,1984,60(4):797-846.
10Hockett,C.A Course in Modern Linguistics[M].New york:Macmillan Company,1958:301.