D. Okpala
发表
D. C. Okpala,
D. Okpala,
1990
.
D. Okpala,
1991
.
D. Okpala,
1989
.
D. Okpala,
C. Nwajinka,
D. Amaefule,
2020
.
D. Okpala,
A. Ikpong,
1992
.
Daniel C. Okpala,
Anny N. Aniekwu,
D. Okpala,
1988
.