300510
Accordingly , any charged particle generates waves , say at time t_0 = 0 and point x_0 = 0 , which will arrive at point x_1 at the instant t_1 = x_1 / c ( here c is the speed of light ) after the emission ( retarded solution ) , and other waves which will arrive at the same place at the instant t_2 = x_1 / c before the emission ( advanced solution ) .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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