The so-called "urban disease" refers to a series of social problems caused by the excessive concentration of population in large cities. It is mainly manifested in the blind expansion of urban planning and construction to the surrounding areas. According to the above definition, which of the following phenomena is not a specific manifestation of urban disease? ['Increased employment pressure.', 'Citizen housing is tight.', 'Crowds of citizens travelling.', 'Declining urban economic strength.']