Final answer:
The correct word to use is 'perceive,' as it means becoming aware of something through the senses, fitting the context where the eyes adjust to darkness and begin to see the furniture's outlines.
Step-by-step explanation:
When the lights went out and visibility was reduced, you mentioned that you were gradually able to discern the outlines of the larger pieces of furniture. The correct word to fill in the blank is perceive. Perceive means to become aware of something through the senses, especially sight, which perfectly fits the context where your eyes adjusted to the darkness and you started to see more clearly. The other options, analyze, envision, and imagine, do not accurately describe the sensory adjustment to the limited light conditions. Envision suggests creating an image in your mind that isn't physically present, imagine also involves creating ideas or pictures in your mind, and analyze is related to examining in detail the constitution or structure of something.