With which words does the German national anthem begin?

EDITORIAL LEARNING AID

Why is this answer correct?

The national anthem begins with the third stanza of the Deutschlandlied: "Einigkeit und Recht und Freiheit …". "Völker, hört die Signale" comes from the Internationale, "Freude schöner Götterfunken" from Schiller's Ode to Joy, and "Deutschland einig Vaterland" is a line from the anthem of the GDR.

Anthem: "Unity and justice and freedom" (3rd stanza).

This translation and explanation are editorial learning aids. The official German wording and answer key govern the examination.