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Because all dates for the Predynastic period are tenuous at best , WMF Petrie developed a system called Sequence Dating by which the relative date , if not the absolute date , of any given Predynastic site can be ascertained by examining the handles on pottery .
 WMF Petrie
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 WMF Petrie