Based on the narrator's emotional state, what is most likely the meaning of sheet?

The answer is B (a flat, open expanse) I know because I got it right

It seems that you have missed the necessary detail for us to answer the given question so I had to look for it. Anyway, here is my answer. Based on the narrator's emotional state, most likely, the meaning of sheet is her life. The poem is written by Robert Frost, and the one that is referred in the poem is a housewife. The housewife somehow is very overwhelmed with the life she is having now for having all the duties and responsibilities. Hope this answers your question.