5.3.2 Thematic Sequence
The thematic sequence is closely related to the information load，meanwhile it varies with text types.The newinform ation in texts is mainly asserted by foreground.Hooper（1979）used the term foreground for the backbone of a narrative.Fleischman took foreground as“those elem ents of a narrative text which are marked somehowas salient or central to themeaning of that text”（Fleischman 1985）.However，foreground and background are not dichotomous or binary distinction.They are patterned along a continuum.“Only in relatively straightforward texts，structured for immediate understanding，are the most salient features likely to be also themost thematically or causally im portant.”（Dry 2002：443）
Exam ple 23：
（1）The Tower of London，seen from the River Thames，with a viewof the water gate called“Traitors'Gate”.The Tower of London is a dominating landmark in central London—in the London Borough of Tower Ham lets—on the eastern border of the City of London，beside the northern bank of the River Thames.［Foreground］
It is often identified with the White Tower，the original stark，square fortress built here by William the Conqueror in 1078.It can be seen，however，as a com plex of several buildings set within the outer defensive walls and moat.［Foreground］
The Tower's prim ary function was as a fortress，a royal palace and a prison（particularly for high status and royal prisoners，such as the Princes in the Tower and the future Queen Elizabeth I）.This last use has led to the phrase“sent to the Tower”meaning“imprisoned”.It has also served as a place of execution and torture，an armory，a treasury，a zoo，a mint，a public records office，and an observatory.［Background］
During the tour，you will notice that some personages and some words have a question mark icon by them（blue and red，respectively）.Clicking on these iconswill take you elsewhere on the Web and provide additional information about the subject.For royalty these linkswill take you to their Royal Genealogies listing，for others to biographical inform ation.For words（usually those associated with architecture）links will take you to its definition at the Webster Hypertext Dictionary.Enjoy your visit！［Instruction］（OETT）(https://www.daowen.com)
Passage（1）invests heavily in foreground，offering newinform ation of the tourist attraction—the Tower of London.Coupling im portance and salience，foreground provides a full viewof the place.In addition，background com plements the history of the spot.Moreover，the last paragraph gives some instructions where visitors can find self-help guidance.
（2）The Great Wall of China was built mainly to protect the Chinese Em pire from the Mongolians and other invaders.Itwas firstbuilt in the 7 th century B.C.when China was still divided into many small states.The construction of the GreatWall had never ceased for nearly all the Chinese fuadal dynasties.［Background］
The Great Wall of China extends 4，000 miles westward from the China Sea town of Shanhaiguan to Gansu Province.［Foreground］The majestic Great Wall was built with wisdom，dedication，blood，sweat and tears.It has been estimated that somewhere in the range of 2 to 3 million Chinese died as part of the centuries-long project of building the wall.［Background］
Nearly everyone has heard of the huge stone wall known as the GreatWall of China.As one of the UNESCO World Heritage Site in China，the Great Wall is not just a wall，but a sym bol of bravery and wisdom of Chinese people.［Evaluation］（TETT）
Different with the former one，Passage（2）provides more background information such as history.In this way，visitors must be ambiguous about the current situation of the Great Wall，only know som ething in ancient tim es.Besides，without any suggestion or instruction，visitorsmight be helpless.
Contrastively，OETT seems to be more direct and effective in information presentation；TETT hard ly presents sufficient foreground information.What'smore，tips on tour are given in OETT butmissing in TETT，indicating OETT is reader-centred but TETT is spot-centred.