23493
Of the 74 principal incidents evaluated in a major study about assassination attempts in the US in the second half of the 20th century , 51 % were undertaken by a handgun , 30 % with a rifle or shotgun , 15 % used knives , and 8 % explosives ( the use of multiple weapons / methods was reported in 16 % of all cases ) .
 US
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 US