1990 has been chosen as the cut - off year for the purpose of this study to differentiate the older buildings from the newer ones that are less than 10 years old and as the i - o concept was introduced in november 1989 注释( 1 ) :由于工贸楼宇的概念是在1989年11月引入，故此本研究选用1990年作为分隔的年份，以区分旧工业楼宇和少于10年楼龄的新工业楼宇。
