How many terrorist attacks involving explosives are preceded by a threat or warning?

Although there is not an exact percentage, it is very low: Terrorist attact tend to be sudden and without warning signs, the act itself is then claimed by terrorism organizations. This has a pretty logical explanation: Giving a warning will surely increase the alertness of the state, so that it would be a lot easier to stop the terrorist before they fulfill their deed.

Urban growth invariably feeds increased commercialization and industrialization. it requires continually expanding land areas. when urbanization rates are high, and countries do not have the institutional and managerial capacities or economic wherewithal to manage such rapid growths, they exert intense pressure on the types and nature of the resulting settlements. they contribute to the development of overcrowded slums and shanty towns without adequate essential services and necessary infrastructure.-by asit k. biswas and cecilia tortajada