Explain why you believe that the courts have found each of the following to either constitute or not constitute a regulatory taking:
(a) A city ordinance reducing the size limit for freestanding signs within the city limits, forcing plaintiff to replace his sign;
(b) A city ordinance prohibiting billboards along roads in residential areas of the city;
(c) The refusal of the Army Corps of Engineers to grant Florida Rock Company a permit to allow it to mine limestone that lay beneath a tract of wetlands.