Zulkarnain Lubis, A.N. Abdalla, Mortaza and Ruzlaini Ghon
American Journal of Engineering and Applied Sciences 2 ( 4 ): 708 - 712 , 2009
Anan Fathi Srouji, Mohd Suberi Ab Halim, Zulkarnain Lubis and Madher Ebrahim Hamdallah
International Business Management 10 ( 6 ): 751 - 758 , 2016
The Social Sciences 9 ( 6 ): 456 - 459 , 2014
Zulkarnain Lubis, Syahbudin Hasibuan and Yusniar Lubis
The Social Sciences 11 ( 3 ): 399 - 406 , 2016
The Social Sciences 12 ( 9 ): 1646 - 1657 , 2017