In the following question a short passage is given with one of the lines in the passage missing and represented by a blank. Select the best out of the four answer choices given, to make the passage complete and coherent. 

Following the sustainable development declaration by the International Union for the Conservation of Nature and Natural Resources (IUCN), the United Nations Environment Programme, and the World Wildlife Fund in 1980, and the announcement regarding sustainable cities in the Toronto Declaration on World Cities and Their Environment in 1990, sustainability has become a key goal in urban planning. Some urban-development paradigms for achieving sustainability have been developed over the past decades. _______________________________ For Taiwanese cities, and most Asian cities, the compact-city paradigm has received increasing attention because these cities develop with significantly limited land resources and infrastructures, and in sensitive environments.