In the prophecy concerning the '70 Weeks' in Daniel 9, what specific event marks the commencement of the countdown, ultimately leading to the Messiah?

A The decree to rebuild the Temple in Jerusalem after its destruction by Babylon. B The anointing of Saul as the first king of Israel. C The commandment to restore and rebuild Jerusalem issued by Artaxerxes I. D The dedication of the second Temple during the reign of Darius.