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Beginning in 1916 , Charles F. Kettering began investigating additives based on two paths , the " high percentage " solution ( where large quantities of ethanol were added ) and the " low percentage " solution ( where only 2 – 4 grams per gallon were needed ) .
 Charles F. Kettering
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
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Text: {0} 
Answer:
 Charles F. Kettering