Which of the following word analysis strategies BEST helps 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