Central and Eastern Europe: the challenge of transition
edited by Regina Cowen Karp
Oxford University Press, 1993
 Buku Teks
Black C.E.
Challenge in Eastern Europe; 12 essays; foreword / by Joseph C. Grew
Rutgers Univ. Press, 1954, 1954
 Buku Teks
Mahathir bin Mohamad, 1925-
The challenge
Pelanduk Publications, 1986
 Buku Teks SO
Serlina
Perbandingan implementasi kampanye marketing public relations Maybelline "Doll it up Challenge" dengan L'oreal Paris "Superstar Me" = Comparison of the implementation of "Doll it up Challenge" campaign by Maybelline and "Superstar Me" by L'oreal Paris
Fakultas Ilmu Sosial dan Ilmu Politik Universitas Indonesia, 2016
 UI - Makalah dan Kertas Kerja
Kouzes, James M.
The leadership challenge
Jossey-Bass, 2002
 Buku Teks SO