Even though all the options seem to mention elements truly present in the stanza, the one that is probably the correct option is: B) The speaker observes the end of the day as life winds down and darkness sets in.
The mentioned elements work as imagery for visualization. The reader can, through this description, picture what the end of the day looks and feels like to the speaker. The bell tolling, the tired worker finally going home, a herd slowing walking on the field... Those images help set the tone for the poem and for the poet's feelings and observations.
