how many months after the riots began across the Khuzestan province were two police officers in Ahvaz killed by separatist gunment?
return the  riots began across the Khuzestan province ;return two police officers in  Ahvaz were killed by separatist gunment ;return when  was  #1 ;return when  was  #2 ;return difference of #3 and  #4 in  months
['select', 'select', 'project', 'project', 'arithmetic']