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There was a bit of a firefight when the 7th Cavalry came upon three Soviet vintage 20 - millimeter anti - aircraft guns , ack - ack guns .
 7th Cavalry: attacker; guns: target
Given event type and trigger, please tell me the arguments of all the listed option. Output format is "name1: role1; name2: role2". 
Event type: attack 
  Option: victim, attacker, place, target, instrument 
Text: {0} 
Answer:
 7th Cavalry: attacker; guns: target