The correct options are
A The identity of spies were hidden.
B They were chosen by the kings directly.
D They gave information to the king about informal messages all around the empire.
The spies were often chosen directly by the kings and acted in secret with their identities unknown to anyone whereas messengers were appointed by the members in the administration for any formal communication between the king and his subjects. The spies also kept the king informed of the events all around the empire.