To decrease the number of crimes in city Y, the city' s Police Commissioner proposed taking some police officers from low-crime districts of the city and moving them to high-crime districts of the city. His proposal is based on city Y crime data that show that the number of crimes in any district of the city decreases when additional police officers are moved into that district. The Police Commissioner's proposal depends on which of the following assumptions? ['There are more low-crime districts than high-crime districts in city Y.', 'The number of crimes committed in all high-crime districts of city Y is more than triple the number of crimes committed in all low-crime districts of city Y.', 'City X experienced a drastic reduction in crime after implementing a proposal similar to that proposed by the Police Commissioner of city Y.', 'Districts of the city from which police officers are removed do not experience significant crime increases shortly after the removal of those officers.']