The 1991 World Book Year Book,
World Book, 1991, 576 p. : ill., 0-7166-0491-4.
.
The 1991 World Book Year Book.
Chicago etc.: World Book, 1991, 576 p. : ill., 0-7166-0491-4.
(1991)
The 1991 World Book Year Book,
Chicago etc.: World Book, 576 p. : ill., 0-7166-0491-4
(1991).
The 1991 World Book Year Book. The Annual Supplement to The World Book Encyclopedia : A Review of the Events of 1990. Chicago etc.: World Book, 576 p. : ill..