Concerning the prophecy in Isaiah 7:14 about a virgin conceiving, what was the primary sign's immediate significance to King Ahaz during the Syro-Ephraimitic War?

A It promised Ahaz military victory over Assyria, securing Judah's dominance. B It guaranteed that the alliance between Syria and Ephraim against Judah would fail within a few years, relieving Ahaz of immediate threat. C It signified the immediate birth of a royal heir who would lead Judah to unprecedented prosperity. D It indicated that Ahaz's dynasty would be replaced by a new royal line more faithful to God.