2568
At the same acoustic power , the rate of chloride formation with 20 kHz ultrasound was greater when a probe with a larger tip area was used , but significantly less than the rate with 900 kHz .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
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