A.Marisa and  Nor'Aini Yusof,  A Study on the Importance of Motivation among the Managers in Construction Companies in Medan.   journal   = {International Journal of Economics and Management Engineering}, [online]. World Academy of Science, Engineering and Technology.
    December 2011, vol. 60(12). 2008 - 2012
    [viewed 25 February 2021]. Available from: https://publications.waset.org/pdf/13080.