The answer is:
B. In Williams's poem, a farmer is the only witness to Icarus's fall, while Auden mentions both a ploughman and a ship.
Both poems, Williams's "Landscape with the Fall of Icarus" and Auden's "Musée des Beaux Arts," mention the ploughman or farmer, but only Auden's work makes reference to a ship. Nevertheless, in both poems, none of the potential witnesses is able to acknowledge the misfortunate moment Icarus falls in to the sea because all of them are engaged in their everyday activities.
The sentence which describes the difference between the two poems is:
C. Auden mentions a ploughman and a ship as witnesses to icarus’s fall, while Williams only mentions a farmer
Both poems are based on a painting that portrays the fall from the sky of the mythological character Icarus. According to the myth, Icarus made wax wings so that he could fly. However, having flown too close to the sun, his wings melted and he fell.
According to Auden's poem, a ploughman and a ship were witnesses to such a tragedy. No one, however, did anything to help poor Icarus:
[...] the ploughman may
Have heard the splash, the forsaken cry,
But for him it was not an important failure; the sun shone
As it had to on the white legs disappearing into the green
Water, and the expensive delicate ship that must have seen
Something amazing, a boy falling out of the sky,
Had somewhere to get to and sailed calmly on.
Williams, on the other hand, only mentions a farmer (who is in fact the same ploughman). He does not mention the ship:
a farmer was ploughing
the whole pageantry
of the year was