context: The city of Detroit and other private-public partnerships have attempted to catalyze the region's growth by facilitating the building and historical rehabilitation of residential high-rises in the downtown, creating a zone that offers many business tax incentives, creating recreational spaces such as the Detroit RiverWalk, Campus Martius Park, Dequindre Cut Greenway, and Green Alleys in Midtown. The city itself has cleared sections of land while retaining a number of historically significant vacant buildings in order to spur redevelopment; though it has struggled with finances, the city issued bonds in 2008 to provide funding for ongoing work to demolish blighted properties. Two years earlier, downtown reported $1.3 billion in restorations and new developments which increased the number of construction jobs in the city. In the decade prior to 2006, downtown gained more than $15 billion in new investment from private and public sectors.
question: ఏ విధమైన భవనాలు నాశనం చేయబడలేదు?
answers: historically significant