Which of the following word analysis strategies best the reader define the word niches in the passage below?

i had been deceived, too, in respect to the shape of the enclosure. in feeling my way i had found many angles, and thus deduced an idea of great irregularity, so potent is the effect of darkness . . the angles were simply those of a few slight depressions, or niches, at odd intervals. the general shape of the prison was square. what i had taken for masonry seemed now to be iron, or some other metal, in huge plates . . the entire surface of this metallic enclosure was [covered] in . . hideous and repulsive devices . .

a.
determining the part of speech
b.
looking for synonyms
c.
looking for affixes
d.
analyzing the mood of the passage