Sommer, Robert
Oxford University Press, 2001
Buku Teks
Abbas Tashakkori, Charles Teddlie
SAGE Publications, 2010
Buku Teks
Leavitt, Fred
C. Brown Publishers , 1991
Buku Teks
Gravetter, Frederick J.
CT Cengage Learning, 2016
Buku Teks
Gravetter, Frederick J.
Cengage, 2018
Buku Teks