Answer:
The words in bold don't start with the same letter as the letter in front of them.
Explanation:
A. Abominable
B. Audi-
C. Ceaselessly
D. Decayed
E. Efface
F. Feeble
G. -iblel-able
H. Impenetrable
1. Imperceptible
J. inaudibly
K. Irreproachable
L. less
M. Lum-
N. Luminous
0. Mal-
P. Malicious
Q. Perceived
R. Somber
S. Torment
T. Wretched