Read the passage from "Ode on a Grecian Urn."Who are these coming to the sacrifice?To what green altar, O mysterious priest,Lead'st thou that heifer lowing at the skies,And all her silken flanks with garlands drest?What little town by river or sea shore,Or mountain-built with peaceful citadel,Is emptied of this folk, this pious morn?And, little town, thy streets for evermoreWill silent be; and not a soul to tellWhy thou art desolate, can e'er return.